LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

GIFT  OK 


Accession      2g.43.69.....       Class ... 


TWENTIETH   CENTURY  TEXT-BOOKS 

EDITED    BY 

A.   F.  NIGHTINGALE,   PH.  D. 

SUPERINTENDENT   OF   HIGH   SCHOOLS,   CHICAGO 


TWENTIETH    CENTURY   TEXT-BOOKS 


THE 

ELEMENTARY  PRINCIPLES 
OF  CHEMISTRY 


BY 


A.  V.    E.   YOUNG 


PROFESSOR   OF   CHEMISTRY   IN   NORTHWESTERN   UNIVERSITY 


"Not  blind 

To  worlds  unthought  of  till  the  searching  mind 
Of  Science  laid  them  open  to  mankind  " 

WORDSWORTH 


NEW    YORK 

D.     APPLETON     AND     COMPANY 
1901 


COPYRIGHT,  1900 
BY  D.   APPLETON  AND  COMPANY 


PREFACE 


THIS  book  on  elementary  chemistry  is  based  on  the  plan 
which,  without  essential  modification,  the  writer  has  been 
following  for  thirteen  years  with  his  classes  beginning  the 
subject.  Its  inception  was  under  the  stimulating  sugges- 
tion of  the  late  Professor  Josiah  P.  Cooke,  of  Harvard  Uni- 
versity, an  early  advocate  of  what  has  been  called  the  quan- 
titative method  in  teaching  the  subject  even  in  elementary 
courses.  The  temerity  of  the  writer  in  thus  offering  to  his 
fellow-students  and  teachers  the  outcome  of  his  personal 
experience  is  due  to  the  hope,  perhaps  egotistic,  that  he 
may  contribute,  in  howsoever  small  a  measure,  to  making 
practicable  and  serviceable  that  which,  he  enthusiastically 
believes,  is  both  scientifically  and  pedagogically  an  improve- 
ment on  the  older  and  still  largely  prevailing  method. 

In  the  preparation  of  the  book  two  things  have  been 
assumed :  first,  that  sufficient  laboratory  facilities  are  pro- 
vided ;  and,  second,  that  the  teacher  has  information  in  the 
subject  beyond  that  which  the  book  itself  supplies.  The 
laboratory  work  by  the  student  is  made  a  large  and  essen- 
tial part  of  the  exposition,  and  it  is  generally  assumed  that 
he  has  performed  the  experiment  illustrative  of  a  topic 
before  he  gives  attention  to  the  fuller  presentation  of  the 
same  in  the  text.  84369 


vi  ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

The  writer  fully  appreciates  the  increased  demand  made 
by  such  a  course  on  the  teacher's  time  and  strength,  and 
he  has  therefore  prepared  to  accompany  this  book  a  teach- 
er's aid,  in  which  he  has  put  whatever  he  has  been  able  of 
suggestions  which  may  be  helpful  and  labor-saving  to  the 
teacher,  but  which  do  not  suitably  find  place  in  a  book 
designed  for  the  use  of  students. 

A.  V.  E.  Y. 

EVANSTON,  ILL.,  June,  1900. 


FOKEWOKD   TO   THE   STUDENT 


You  are  about  to  enter  upon  the  study  of  a  branch  of 
natural  science,  perhaps  the  first  to  which  experience  has 
brought  you.  If  I  am  to  have  the  privilege,  shared  with 
your  teacher,  of  being  your  guide  in  this,  I  beg  the  addi- 
tional privilege  of  addressing  a  word  to  you,  at  the  outset 
of  your  study,  in  a  purely  personal  manner  and  free  of  the 
formality  of  authorship.  As  a  lover  of  nature,  whether  in 
the  aspect  revealed  by  science,  or  in  that  which  lies  open  to 
him  who  has  eyes  to  see  and  soul  to  feel,  and  as  one  to 
whom  science  study  has  brought  much  genuine  enjoyment, 
I  would  that  to  you  also  this  study  might  be  not  a  task 
only,  even  though  interesting  and  profitable,  but  a  source 
of  real  pleasure. 

A  large  portion  of  your  time  will  be  given  to  experi- 
ments. They  may  seem  tedious  at  times,  and  may  test  your 
patience ;  but  they  are  designed  to  teach,  not  to  amuse, 
and,  in  order  to  teach,  they  must  be  performed  studiously 
and  thoughtfully.  It  may  be  hoped  that  you  will  find  a 
pleasure  added  to  mental  activity  in  the  accompanying  use 
of  the  hands. 

Again,  your  experiments  are  generally  to  be  thought  of 
as  giving  you  not  proof  of  laws,  but  illustration,  as  aid  to 

clear  ideas.     In  my  own  classes,  I  like  that  the  student 

vii 


viii        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

should,  so  far  as  practicable,  get  the  first  notion  of  a  topic 
through  his  own  observation,  instead  of  being  told  in  pre- 
vious explanation  what  he  is  to  see.  In  this  way,  I  believe, 
there  may  come  to  him  just  a  taste  of  the  keen  pleasure  of 
discovery  that  comes  to  the  investigator  and  pioneer. 

I  would  reckon  one  opportunity  of  profit  from  a  course 
in  physical  science  as  lost  to  that  student  who  fails  to 
acquire  some  increased  measure  of  respect  for  the  teachings 
of  experience,  which  should  serve  him  to  good  purpose,  if 
rightly  applied,  in  the  daily  conduct  of  life. 

Moreover,  he  should  learn  respect  for  material  things, 
finding  in  them  not  alone  facts,  useful  of  application  in 
practical  life,  and  gratifying  to  the  inborn  curiosity  of  the 
human  mind  to  know,  but  likewise  things  worthy  of  oft- 
repeated  contemplation,  and  gratifying  to  the- intellect  to 
admire.  The  lover  of  nature  is  not  content  with  one  view 
of  a  beautiful  landscape;  nor  is  the  lover  of  art  content 
with  one  look  at  the  handiwork  of  a  great  painter  or  sculptor, 
but  he  returns  with  fresh  joy  to  contemplate  the  beauty 
which  it  embodies.  Yet  this  is  the  work  of  the  human 
hand  and  intellect.  Likewise  the  student  of  natural  science, 
I  am  sure,  may,  if  he  will,  add  much  to  the  pleasure  of  his 
work  and  to  its  ennobling  influence  by  finding  in  the  mate- 
rial things  revealed  by  his  science  the  handiwork  and  em- 
bodied thought  of  the  mightiest  of  creators,  worthy  of 
repeated  contemplation  and  productive  of  the  noblest 
pleasure. 

"  God  is  the  Perfect  Poet, 
Who  in  creation  acts  his  own  conceptions." 

ROBERT  BROWNING,  in  Paracelsus. 

A.  V.  E.  Y. 


SCHEME   OF  TOPICS 

[The  numbers  following  the  topics  refer  to  marginal  numbers  in  the  text, 
which  are  the  same  for  the  same  topics  in  both  Part  I  and  Part  II.] 

CHAPTER   I.     Nos.  1-33 
INTRODUCTORY 

In  Physical  Phenomena  two  things  distinguished  : 
Matter  and  Energy. 
Different  kinds  of  Matter  =  Substances. 
Transformation  of  Substances. 

Definition  and  Identification  of  Substances  by  Physical  and 
Chemical  Properties 

A.  Physical  Properties  (with  special  reference  to  Identification) : 

1.  Taste. 

2.  Odor. 

3.  Relative  Hardness. 

4.  Form  (crystalline). 

5.  Mass  (measured  by  weight). 

6.  Volume. 

7.  Specific  Gravity,  No.  7. 

(Comparative  weight.) 

8.  Behavior  toward  Light : 

As  to  Color,  Luster,  Transparency,  Opacity. 

9.  Behavior  toward  Electricity. 
10.  Behavior  toward  Magnetism. 

a.  Solids. 

Fusion,  solidification,  10. 

b.  Liquids. 

Boiling,  11. 


11.  Behavior  toward  Heat « 


Distillation,  12. 
Sublimation,  12. 
c.  Gases. 

Burning  or  combustion. 
Chemical  change. 


x  ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

B.  Chemical  Properties,  13. 

Transformation  of  Substances. 
Behavior  toward  Other  Substances. 

C.  Physico-Chemical  Properties. 

1.  Allotropism,  13. 

2.  Solution,  21. 

Study  of  Chemical  Change,  15-18. 

Additional  Physical  Properties 
Crystallization,  21/4. 

Amorphism,  Polymorphism,  Isomorphism,  21/6. 

Water  of  Crystallization,  21/7. 
Efflorescence,  21  /8. 
Deliquescence,  21/8. 

(Hygroscopic.) 
Heat  of  Solution,  22. 
Melting  Point,  23. 

Freezing  Point. 

Surfusion. 
Boiling  Point,  24. 

Conditions  affecting. 

Chemistry  is  loth  : 

A.  Static. 

Description,  Identification,  Classification  of  Definite  Chemical 

Substances. 

Qualitative  Analysis,  26. 
Quantitative  Analysis,  26. 

B.  Dynamic,  26. 

Factors 
Products 


Chemical  Change,  or 
of  -{  Reaction,  or 


Laws 

Agency— i.  e., 

VM,       .  /-.i_-     i   *  no    -.L  ^  Interaction. 

Chemism  or  Chemical  Affinity 

Energetics 

All  Substances  classified  into  : 

a.  Elements,  27,  and 

b.  Compounds  (Mechanical  Mixtures,  28). 

Compounds  classified  (in  part),  30  : 
Acids,  Bases,  Salts. 

Chemical  Changes  classified  (in  part),  31  : 
a.  Analytic  (Decomposition). 
&.  Synthetic  (Combination). 

c.  Metathetic  or  Mixed  (Exchange). 

Substitution. 

'  I 


SCHEME  OP  TOPICS  xi 

CHAPTER  II.    Nos.  34-60. 
THE  FUNDAMENTAL  QUANTITATIVE  LAWS  OF  CHEMICAL  ACTION 

1.  The  Law  of  Persistence  of  Mass  (Lavoisier),  34. 

2.  The  Law  of  Fixed  Proportions  (Proust),  37. 

3.  The  Law  of  Multiple  Proportions  (Dalton),  40. 

4.  The  Law  of  Equivalent  Proportions  (Richter  and  Wenzel),  41. 

Corollary  I.  Equivalent  and  Combining  Weights  of  the  Elements, 

42. 

Corollary  II.  Combining  Weights  of  Compounds,  45. 
Corollary  III.  Active  Masses,  the  Multiples  of  Combining  Weights, 

46. 

5.  The  Law  of  Gas-volumetric  Proportions  (Gay-Lussac),  47. 

Some  Illustrations  of  Relative  Quantities  in  Combination,  49. 

6.  The  Law  of  Persistence  of  Energy  applied  to  Chemical  Phenomena, 

50. 
The  Law  of  Constant  Heat  Summation  (Hess),  55. 


CHAPTER  III.     Nos.  61-65 

1.  The  System  of  Combining  Weights,  61. 

2.  The  System  of  Notation,  62.  , 

(a)  For  Elements. 

(b)  For  Compounds. 

3.  Chemical  Equations,  63. 

4.  Stoichiometry,  64. 

5.  Chemical  Nomenclature,  65. 
Problems. 


CHAPTER  IV.     Nos.  66,  67 
RELATION  BETWEEN  VOLUME,  PRESSURE,  AND  TEMPERATURE  OF  GASES 

I.  The  Law  of  Boyle. 

Relation  between  Volume  and  Pressure  of  Gases. 

Corollary. 
II.  The  Law  of  Charles. 

Relation  between  Volume  and  Temperature  of  Gases. 
Corollary. 

Note  I  and  II. 


xii          ELEMENTARY  PRINCIPLES  OP  CHEMISTRY 


CHAPTER  V.    Nos.  68-141 

RELATION  BETWEEN  EQUIVALENT  AND  COMBINING  WEIGHTS  AND  CER- 
TAIN SPECIFIC  PROPERTIES 

1.  The  Law  of  Gay-Lussac,  71-90. 

Relation  between  Equivalent  and  Combining  Weights  of  Gases, 

Elementary  and  Compound,  and  their  Specific  Gravities. 
Note  I,  91. 
Note  II,  92. 

2.  The  Law  of  Dulong  and  Petit,  95-102. 

Relation   between   Equivalent   and  Combining  Weights  of  Ele- 
mentary Solids  and  their  Specific  Heats. 
Corollary,  103. 

3.  The  Law  of  Mitscherlich,  107. 

Relation  between  Composition,  and  hence  Combining  Weight,  and 
Specific — i.  e.  Crystalline — Form. 

4.  The  Law  of  Raoult  (1),  109-123. 

Relation  between  Combining  Weights  of  Solutes  and  Specific  De- 
pressions of  the  Freezing  Point  in  Specified  Solvent. 

5.  The  Law  of  Raoult  (2),  124-135. 

Relation  between  Combining  Weights  of  Solutes  and  Elevations 

of  Boiling  Temperature  in  Specified  Solvent. 
Summary,  136. 

CHAPTER  VI.     Nos.  142-156 

METHOD  OF  DETERMINING  EQUIVALENT  (144)  AND  COMBINING  WEIGHTS 
(150)  OF  ELEMENTS  AND  FORMULAS  (153)  OF  COMPOUNDS 

Problems,  156. 

CHAPTER  VII.     Nos.  157-186 
THE  ATOMIC  THEORY  :  ITS  FUNDAMENTAL  ASSUMPTIONS 

.1.  The  Molecular  Constitution  of  Matter,  163. 

2.  The  Kinetic  Theory  of  Gases,  164. 

3.  Avogadro's  Hypothesis,  165. 

4.  The  Chemical  Definition  of  a  Molecule,  166. 

5.  As  to  Molecular  Weights,  167. 

6.  The  Divisibility  of  the  Molecule  of  a  Compound,  168. 

7.  The  Divisibility  of  the  Molecule  of  an  Element,  169. 

8.  The  Atom  defined,  171. 


SCHEME  OF  TOPICS  xiii 

9.  As  to  Atomic  Weights,  173. 

10.  As  to  Heat  Capacity  of  Atoms,  175. 

11.  As  to  Raoult's  Laws,  176. 

12.  As  to  Structure  of  Molecules,  177. 

Isomers  (179),  Polymers  (179),  Metamers  (180). 

13.  As  to  Space  Relations  of  Atoms,  or  Stereo-Isomerism,  183. 


CHAPTER  VIII.     Nos.  187-641 

RELATION  BETWEEN  THE  PROPERTIES  OF  THE  ELEMENTS  IN  GENERAL 
AND  THEIR  COMBINING  WEIGHTS 

Description  of  the  First  Twenty-Jive  .Elements  and  some  of 

their  Compounds 
Of  the  Elements  Collectively,  188. 
.  Hydrogen,  200.  \^>.  Nitrogen,  306. 

2.  Lithium,  210.  Oxides,  312-325. 

3.  Glucinum,  216.  Nitric  Acid,  326. 

4.  Boron,  220.  Nitrates,  333. 

Borax  bead,  228.  Ammonia,  334. 

^  5.  Carbon,  234.  Other  Compounds,  339. 

5a.   Carbon  Dioxide,  259.  Relation    to  Living  Things, 

5b.  Carbonates,  269.  344. 
5c.  Carbon  Monoxide,  272.  /^7.  Oxygen,  350. 

5d.  Hydrocarbons,  274.  Ozone,  358. 

5e.   Flame,  284,  Part  II.  Hydrogen  Dioxide,  366. 

5f.   Petroleum,  293.  Water,  368. 

5g.  Coal,  298.  Natural  Waters,  371. 

5h.  Coal  Gas,  301.  Purification  of  Water,  378. 
5i.    Destructive  Distillation 
of  Wood,  303. 

/  B.  The  Atmosphere,  388. 

C.  Argon,  396. 

.      Other  New  Elements  in  the  Atmosphere,  398. 
V  8.  Fluorine,  401. 
9.  Sodium,  407. 

9a.   Sodium  Chloride,  411. 
9b.  Sodium  Carbonate,  413. 
9c.  Sodium  Hydroxide,  419. 

D.  General  Survey,  422. 

E.  Valence,  434. 

Review  Problems,  441/|. 


1 


ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


15.  Chlorine,  527. 

15a.  Oxides  and  Acids  of, 
536. 

15b.  Bromine  and  Iodine, 
541A. 

15c.  Manufacture  of  Chlo- 
rine and  Bleaching 
Powder,  542. 

16.  Potassium,  549. 


10.  Magnesium,  442. 

11.  Aluminium,  448. 

lla.  Manufacture  of,  462. 

12.  Silicon,  466. 

'  12a.  Uses  of  Silicates,  476. 

13.  Phosphorus,  484. 

13a.  Oxides  and  Acids  of, 
492. 

13b.  Other  Compounds  of, 
496. 

13c.  Manufacture  of  Phos- 
phorus and  Matches 
498. 
]  14.  Sulphur,  507, 

14a.  Compounds  with  Hy- 
drogen and  Chlo- 
rine, 510. 

/  14b.  Oxides  and  Acids  of, 
514. 

14c.  Manufacture  of  Sul- 
phuric Acid,  523. 

F.  Gunpowder  and  Some  Other  Explosives,  555. 
17.  Calcium,  577. 

17a.  Mortar  and  Other  Cements,  585. 
Review  Problems,  588/i. 

G.  General  Survey,  589. 

21-25.  Chromium,  Manganese,  Iron,  Nickel,  Cobalt,  591. 

23a.  Commercial  Iron,  607. 
H.  The  Law  of  Periodicity,  620. 

LIST  OF  ELEMENTS  IN  ALPHABETICAL  ORDER,  643. 
LIST  OF  ELEMENTS  IN  NATURAL  ORDER,  644. 


THE   ELEMENTARY   PRINCIPLES 
OF   CHEMISTRY 


PAR  T    I 


CHAPTER  I 

INTRODUCTION 

Matter,  energy,  substances. — In  physical  phenomena  the  1* 
student  of  nature  has  learned  to  distinguish  two  things, 
Matter  and  Energy.  Matter  is  all  that  which  occupies 
space,  has  weight,  and  is  acted  upon  by  various  agents ; 
for  example,  earth,  water,  air,  iron,  wood,  and  salt.  Energy 
is  that  which  brings  about  change  in  things ;  change  in 
position — that  is,  motion — as  when  a  body  falls  to  the 
earth;  or  change  in  nature,  as  when  iron  rusts,  or  wood 
burns,  or  water  freezes.  Energy  is  therefore  the  general 
name,  not  for  any  particular  agent,  but  for  all  agents  that 
bring  about  the  specified  changes.  Thus,  gravitation,  heat, 
electricity,  magnetism,  and  light  are  only  different  forms 
or  conditions  of  energy.  Likewise,  the  very  many  things 
familiarly  recognized,  such  as  water,  air,  coal,  copper,  silver, 
gold,  and  others  not  so  familiar,  are  simply  different  kinds 
of  matter ;  to  designate  these  is  used  the  term,  substances. 

Substances  are  not  permanent. — Now,  it  is  readily  recog-  2 
nized  as  a  fact  of  common  observation,  that  substances,  in 
many  instances  at  least,  are  not  permanent,  but  are  subject 

*  The  marginal  numbers  are  the  same  for  the  same  topics  in  both 
. 


2  ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

to  change ;  and  furthermore,  that  the  changes  often  result 
in  the  disappearance  of  the  original  substances.  Thus 
water  may  lose  its  liquid  form  and  become  solid,  in  which 
condition  we  call  it  ice ;  or  it  may  become  gaseous,  in 
which  condition  we  call  it  steam  or  vapor.  Wood  rots  and 
iron  rusts,  and  in  so  doing  both  lose  many  of  the  properties 
which  make  them  useful.  Wood  and  coal  burn,  and  thus 
are  converted  into  something  which  is  neither  wood  nor 
coal.  A  lump  of  sugar,  or  of  salt,  when  dropped  into  water, 
completely  disappears  so  far  as  we  can  see.  And  many 
similar  observations  might  be  cited.  But,  evidently,  we  can 
not  make  even  the  simple  observation  that  iron  ceases  to 
be  iron  when  it  rusts,  or  that  wood  ceases  to  be  wood  when 
it  burns,  or,  in  general,  that  any  substance,  A,  ceases  to 
be  A,  or  becomes  some  other  substance,  B,  unless  we  have 
some  means  of  identifying  the  substances,  A  and  B,  and 
distinguishing  between  them ;  and  these  constitute,  in  part 
at  least,  the  subject-matter  of  Chemistry.  For  present  pur- 
poses, then,  we  may  define  Chemistry  as  that  branch  of 
physical  science  which  deals  primarily  with  the  properties 
and  transformations  of  substances.  Physics,  on  the  other 
hand,  deals  primarily  with  the  several  kinds  of  energy  and 
their  transformations.  The  two  sciences  are  therefore 
closely  related,  and  many  phenomena  may  be  considered  as 
properly  in  one  as  in  the  other ;  and  some  must,  indeed,  be 
considered  in  both. 

Identification  of  substances. — We  proceed,  therefore,  to 
study  somewhat  in  detail  the  identification  of  substances. 
Broadly  speaking,  a  substance  can  be  identified  only  by  its 
totality  of  properties,  but  in  practice  it  is  possible  to  use 
selected  properties,  since  we  have  learned  by  experience 
that  these  are  accompanied  by  the  others  which  make  up 
the  total.  Of  the  properties  of  a  substance,  we  designate 
as  physical  those  which  involve  no  change  in  the  identity 
of  the  substance  ;  as  chemical,  those  which  do  involve  such 
change.  But  here,  as  often  when  we  attempt  to  classify 


INTRODUCTION  3 

or  define  the  things  of  nature,  we  find  those  which  can  not 
be  placed  satisfactorily  in  one  or  the  other  class,  since 
they  partake  of  the  character  of  both  ;  and  so  we  shall  find 
it  convenient  to  recognize  properties  of  a  third  class,  and 
to  designate  them  as  the  physico-chemical. 

1.  Physical  Properties 

Among  the  physical  properties  useful  for  identification  4 
may  be  cited :  taste,  odor,  relative  hardness,  form  (crystal- 
line), specific  gravity  (i.  e.,  the  relation  between  weight  and 
volume) ;  also  behavior  toward  (1)  light,  as  to  color,  luster, 
opacity,  etc. ;  (2)  toward  electricity ;  (3)  toward  magnet- 
ism ;  (4)  toward  heat. 

The  chemical  properties  may  be  described,  with  but  few  5 
exceptions,  as  the  behavior  toward  other  substances ;  while 
the  phenomena  of  solution  and  of  allotropism  may  serve  as 
illustrations  of  physico-chemical  properties. 

Before  presenting  formal  statements  and  definitions  con- 
cerning these  items,  it  is  best  that  they  be  studied  by  prac- 
tical illustrations ;  and  so  sulphur  is  taken  up  first,  as  an 
object-lesson  in  description  and  identification  of  substances 
(see  Chapter  I,  Part  II).  Following  the  observations  and 
illustrative  experiments  made  by  the  student  in  the  labora- 
tory, the  matter  now  to  be  presented  may  be  considered  as 
a  review  and  summary  of  the  corresponding  topics,  with 
some  added  information,  impracticable  of  illustration. 

Taste. — Taste  is  of  limited  applicability  for  purposes  of  6 
identification,  and  in  the  chemical  laboratory  should  be 
used  with  only  the  utmost  caution,  as  many  substances  are 
extremely  poisonous. 

Odor. — Odor  is  more  often  serviceable,  but  likewise  must 
be  used  with  caution. 

Form. — By  form  in  this  connection  is  meant  only  crys- 
talline form — that  is,  definable,  geometric  form,  which,  as 
will  be  seen  later,  is  often  characteristic. 
2 


4        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

7  Specific  gravity. — The  specific  gravity  of  a  substance  is 
the  ratio  of  the  weight  of  some  sample  of  it  divided  by 
the  weight  of  an  equal  volume  of  some  standard  substance. 
Water  is  taken  as  the  standard  for  solids  and  liquids,  or, 
more  strictly  speaking,   water  at  its  maximum   density 
(temperature  4°  C.).     For  gases,  both  hydrogen  and  air  are 
used ;  the  former  is  preferred  in  this  study,  and  may  be 
understood  as  the  standard  for  gases  unless  it  is  otherwise 
specified.     Inasmuch  as  the  specific  gravity  of  air  referred 
to  hydrogen  is  14.40, -it  is  easy  to~pa-sHfrom  one  scale  to  the 
other  by  the  use  of  this  factor. 

8  Your  experiment  with  sulphur  has  given  illustration  of 
&  method  for  determining  the  specific  gravity  of  solids 
which  are  not  soluble  in  water.     If  the  solid  dissolves  in 
water,  some  other  liquid  must  be  used  in  which  the  sub- 
stance is  insoluble,  and  of  which  the  specific  gravity  is 
known.     Another  method  is  based  on  the  principle  that  a 
body  when  suspended  and  immersed  in  a  liquid  weighs  less 
than  when  weighed  in  air  simply,  and  less  by  a  quantity 
equal  to  the  weight  of  the  liquid  displaced. 

Since  liquids  and  gases  may  completely  fill  their  con- 
taining vessel,  their  specific  gravity  may  be  determined  by 
weighing  successively  the  vessel  when  empty,  when  filled 
with  the  standard,  and  when  filled  with  the  substance  in 
question. 

9  Electrification, — The  electrification  of  sulphur  by  fric- 
tion, so  that  it  attracts  particles  of  matter,  is  a  minor  item. 
Of  the  same  order  also,  is  the  familiar  observation  that 
iron  is  attracted  by  the  magnet. 

The  facts  as  to  color,  luster,  opacity,  or  transparency 
usually  appear  simply  on  inspection. 

10  Behavior  toward  heat. — The  behavior  toward  heat  is  of 
prime  importance.  Three  conditions  of  matter  are  recog- 
nized— the  solid,  the  liquid,  and  the  gaseous.  These  are 
dependent  on  the  temperature,  or  on  the  temperature  and 
the  pressure  combined. 


INTRODUCTION  5 

Fusion  or  melting  is  changing  a  solid  into  a  liquid  by 
the  agency  of  heat.  Freezing,  solidification,  or  congelation 
is  changing  into  the  solid  condition  from  the  liquid,  some- 
times from  the  gaseous,  by  the  withdrawal  of  heat.  The 
behavior  of  sulphur,  which  you  have  noted,  is  peculiar  in 
that  the  continued  application  of  heat  after  fusion  causes 
the  liquid  first  to  become  semi-solid  and  then  to  regain  its 
fluidity.  The  temperature  at  which  fusion  and  solidifica- 
tion take  place  is  definite  and  constant  for  a  given  sub- 
stance, and  hence  offers  a  valuable  feature  for  identifica- 
tion. Its  determination  will  be  considered  later. 

Boiling  or  ebullition  is  the  formation  in  a  liquid  of  bub-  11 
bles  of  its  own  vapor.  Evaporation — that  is,  the  conver- 
sion of  a  liquid  into  vapor  at  its  surface  only — takes  place 
at  indefinite  temperatures,  even  much  below  that  of  boil- 
ing. But  bubbles  of  vapor  form  only  in  definite  condi- 
tions, and  therefore  the  temperature  at  which  boiling  takes 
place  is  also  a  valued  feature,  which  later  will  be  studied 
in  detail. 

Distillation  (for  experimental  illustration  see  not  only  12 
Exps.  11  and  12,  but  also  20/j  and  24/5 ,  and  Appendix,  18) 
is  the  conversion  of  a  solid  or  of  a  liquid  into  vapor  by  heat- 
ing, and  this  vapor  in  turn  into  a  solid  or  liquid  by  cooling. 
It  is  serviceable  in  separating  volatile  from  non-volatile  sub- 
stances, or  substances  differing  in  degree  of  volatility,  and 
is  therefore  often  a  valuable  means  of  purification.  That 
which  is  separated  by  distillation  and  condensed  is  called 
the  distillate.  Some  substances  may  be  converted  from 
solid  to  vapor  and  back  to  solid  without  passing  through 
the  liquid  condition.  This  operation  is  called  sublimation, 
and  the  condensed  portion  is  called  the  sublimate. 

In  nature  the  formation  of  rain  may  be  considered  as  distillation 
on  an  enormous  scale,  since  water  passes  from  the  surface  of  the  sea 
and  other  bodies  of  water  into  the  atmosphere  as  a  vapor,  is  subse- 
quently condensed  into  liquid  form,  and  falls  to  the  earth  again  as 
drops  of  rain.  Or,  the  water  vapor  of  the  atmosphere  may  condense 


6  ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

directly  to  the  solid  snowflake  or  to  the  frost  upon  the  window  pane, 
and  these  we  may  think  of  as  natural  sublimates. 

Distillation  and  sublimation  are  used  also  in  many  industrial  opera- 
tions— for  example,  in  the  manufacture  of  alcohol,  the  refining  of 
petroleum,  of  sulphur,  and  of  iodine. 

2.  Chemical  Properties 

13  Essential  feature. — Returning  to  the  observations  with 
sulphur :  you  have  seen  that,  if  the  heating  is  continued 
beyond  the  boiling  point,  the  sulphur  finally  takes  fire, 
burning  with  a  pale  bluish  flame ;  that  in  consequence  of 
this  change,  called  combustion,  the  sulphur  disappears ;  that 
a  substance  appears  which  is  gaseous  at  the  ordinary  tem- 
perature, has  a  peculiar,  stifling  odor,  changes  blue  litmus 
paper  to  red,  and  is  thus  a  substance  distinctly  different 
from  the  sulphur  itself.  This  change  is  a  chemical  one,  its 
essential  feature  being  the  production  of  a  substance  other 
than  the  original — it  is  a  change  of  identity  ;  whereas  the 
other  changes  already  noted,  electrification,  fusion,  solid- 
ification, boiling,  sublimation,  and  distillation,  all  physical, 
have  left  the  substance  still  sulphur.  The  peculiar  product 
obtained  by  turning  the  liquid  sulphur  at  about  its  boiling 
point  into  cold  water  certainly  differs  in  some  of  its  prop- 
erties from  the  original  substance.  On  inspection  you  hardly 
recognize  it  as  sulphur,  yet  on  standing^t  passes  back  into 
the  brittle  condition  without  a  change  in  weight,  and  en 
burning  it  yields  the  same  gaseous  product  that  the  brittle 
sulphur  does.  Such  a  change,  considerable  yet  not  suf- 
ficient to  constitute  a  change  in  identity,  is  called  allo- 
tropic  ;  and  the  plastic  or  amorphous  substance  and  the 
brittle  or  crystalline  are  said  to.  be  allotropic  forms  of  sul- 
phur. Further  illustration  of  chemical  change  you  have 
seen  in  the  production  of  iron  sulphide  from  iron  and 
sulphur,  zinc  sulphide  from  zinc  and  sulphur,  hydrogen 
sulphide  from  hydrochloric  acid  and  iron  and  zinc  sul- 
phides. 


INTRODUCTION  7 

Secondary  features.  —  You  may  also  note  as  secondary 
differences  between  physical  and  chemical  changes,  that  the 
former  may  involve  but  a  single  substance,  whereas  chem- 
ical changes  must  involve  at  least  two,  and  generally  in- 
volve more  than  two.  There  are  a  few,  but  only  a  few, 
changes  which  fall  under  the  general  form  :  substance  A 
becomes  substance  B,  or,  more  briefly  expressed,  A  =  B. 
Therefore  the  chemical  properties  of  a  substance  may  be 
generally  described  as  its  behavior  toward  other  substances. 
Again,  the  physical  changes  are  often  reversible  by  revers- 
ing the  conditions  ;  thus  sulphur  changes  from  solid  to 
liquid  and  then  to  vapor  by  rise  of  temperature,  and  then 
a  fall  of  temperature  reverses  the  changes.  On  the  other 
hand,  if  the  temperature  be  raised  until  the  sulphur  burns 
—  that  is,  until  chemical  action  takes  place  and  the  new 
substance,  sulphur  dioxide,  is  formed  —  this  change  is  not 
reversible  ;  that  is,  the  sulphur  can  not  be  recovered  by 
cooling  the  gas. 

3.  Additional  Illustrations  of  Chemical  Change 

The  additional  illustrations  of  chemical  change  have 
brought  to  your  attention  the  four  types,  which  may  be 
given  general  expression  in  the  following  concise  equation 
forms,  and  which  for  the 


dwelt  upon  in  connection  with  the  illustrative  experiments  : 

(1)  ^r^FTT=  AB  (compositiop).  15 

(2)  "AB  —  A  +  B  (decomposition).  16 

(3)  A  +  BC  =  B.+  AC  (substitution).  17 

(4)  AB  +  CD  =  AC  -f  BD  (double  exchange).  18 

4.  Additional  Illustrations  of  Physical  Properties 

Solution.  —  We  proceed  now  further  to  consider  some  of  21 
the  physical  properties.     Solution  is  the  conversion  of  a 
solid  or  of  a  gas  into  a  liquid  by  the  action  of  a  liquid, 


8  ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

The  term  is  also  applied  to  the  mixing  of  one  liquid  with 
another.  The  substance  dissolved  is  called  the  solute,  the 
liquid  which  effects  the  solution  the  solvent,  and,  unfor- 
tunately for  clearness,  the  mixture  of  these  two — that  is, 
the  result  obtained  by  dissolving — is  called  the  solution. 
The  phenomenon  of  solution  has  practically  a  limitation, 
qualitative  in  character — that  is  to  say,  some  substances 
dissolve  in  some  solvents  and  not  in  others,  while  some  are 
practically  insoluble  in  all  solvents.  Thus  sugar,  common 
salt,  alum,  and  copper  sulphate  dissolve  in  water,  but  not 
in  carbon  disulphide  ;  while  sulphur  dissolves  in  the  latter 
(see  Exp.  12/2),  but  not  in  water.  And  yet  those  sub- 
stances commonly  reckoned  as  the  most  insoluble  do,  in 
many  instances,  dissolve  in  minute  quantity.  Thus,  for  in- 
stance, sand,  limestone,  and  glass  would  in  ordinary  expe- 
rience be  thought  insoluble  in  water,  yet  they  do  appre- 
ciably dissolve. 

21/1  Solution  plays  an  important  part,  often  on  a  vast  scale,  in  the  pro- 
cesses of  nature,  and  in  these,  water  is  the  great  solvent.  Water  pass- 
ing through  the  atmosphere  and  over  or  through  the  earth's  crust  dis- 
solves many  substances  in  quantities — small  perhaps  in  proportion  to 
the  quantity  of  the  solvent,  yet  large  in  the  aggregate,  since  the  quan- 
tity of  water  is  enormous.  These  ultimately,  at  least  in  large  part, 
reach  the  sea,  which  thus  becomes  a  vast  reservoir,  not  only  of  water, 
but  also  of  soluble  matter  from  the  solid  portion  of  the  earth's  crust. 
This  is  the  most  stupendous  instance  of  the  phenomenon  of  solution 
within  our  observation.  In  the  vital  processes  of  the  plant  and  of  the 
animal,  solution  is  of  great  importance,  serving  to  bring  the  constituents 
of  the  food  into  condition  suitable  for  distribution  and  assimilation  in 
the  different  parts  of  the  organism. 

21/2  Solution  is  an  operation  of  prime  importance  also  in  the  industrial 
'  arts  as  well  as  in  the  laboratory.  It  is  used  not  only  to  separate  soluble 
from  insoluble  substances  and  substances  of  different  degrees  of  solu- 
bility, and  consequently  as  a  means  of  purification,  but  also  to  bring 
about  a  condition  suitable  for  some  other  operation  or  change.  The 
refining  of  sugar  is  one  of  the  innumerable  instances. 

21/3  The  property  of  solubility  or  insolubility,  or  the  degree 
of  solubility,  is  also  of  great  practical  value  in  the  identifi- 


INTRODUCTION  9 

cation  of  substances.  The  quantity  of  a  given  substance 
which  a  definite  quantity,  say  one  hundred  grams,  of  a 
given  solvent  can  dissolve  is  limited,  and  is  dependent  on 
temperature,  and,  in  the  case  of  gases,  on  pressure  also ; 
but  for  a  definite  temperature  (and  pressure)  the  quantity 
is  definite.  The  solubility  of  solids  generally  increases  with 
increase  of  temperature,  but  in  some  instances  it  decreases. 
The  solubility  of  gases  diminishes  with  increase  of  temper- 
ature, and  it  increases  with  increase  of  pressure.  A  solvent, 
when  it  has  dissolved  the  maximum  of  a  given  substance,  is 
said  to  be  saturated.  Unsaturated  solutions  of  solid  or 
non-volatile  substances  may  be  concentrated  by  evaporat- 
ing the  solvent  (see  Exp.  21/4),  and  the  solute  may  be 
recovered,  often  unchanged,  by  making  the  evaporation 
complete  (see  Exps.  17/i  b  and  18/A). 

Crystallization. — If  saturated  or  nearly  saturated  solu-  21/4 
tions  remain  undisturbed,  so  that  slow  cooling  and  evapora- 
tion may  take  place,  the  solid  in  many  instances  separates 
in  definite  geometric  forms,  as  you  saw  in  your  own  experi- 
ments with  alum  and  copper  sulphate.  This  is  crystalliza- 
tion. It  may  accompany  solidification,  not  only  from  the 
state  of  solution,  but  also  of  fusion  (seen  in  the  sulphur  ex- 
periments, !Sros.  11  and  12,  and  12/i),  and  even  from  the 
gaseous  condition  (seen  in  the  experiment  with  iodine,  No. 
20/i ,  the  sublimate  of  which  is  beautifully  crystalline).  In 
the  crystallization  of  mixtures  each  individual  substance 
crystallizes  by  itself,  in  its  own  peculiar  form,  and  therefore 
crystallization  is  a  most  important  means  of  separation  and 
purification.  Furthermore,  the  peculiarities  of  form — that 
is,  the  shape  and  disposition  of  the  faces,  the  dimension  of 
the  angles,  etc. — are  definite  and  constant  characteristics 
of  the  substance,  and  therefore  of  great  value  in  identifi- 
cation. 

.Crystallization  on  the  large  scale  finds  abundant  illustration  in   21/5 
nature,  since  many  constituents  of  the  earth's  crust  exist  in  crystalline 
condition,  either  in  large  masses  of  crystalline  structure,  like  granite, 


10          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

marble,  etc.,  or  as  distinct  individual  crystals  like  the  diamond,  ruby, 
emerald,  and  many  other  valued  gems.  Many  manufactured  products 
also  appear  in  crystalline  condition,  of  which  sugar  and  salt  may  be 
cited  as  examples. 

21/6  Substances  when  they  do  not  show  this  definite  geomet- 
ric or  crystalline  form  are  said  to  be  in  the  amorphous  con- 
dition. Some  substances  are  capable  of  crystallizing  in  two 
or  more  distinctly  different  forms.  They  are  said  to  be 
polymorphous,  or,  if  they  exhibit  only  two  forms,  dimor- 
phous. This  property  you  have  seen  in  the  two  crystal- 
line forms  of  sulphur  (see  Exps.  12/1?  and  12/2).  On  the 
other  hand,  some  instances  are  found  of  different  substances 
exhibiting  the  same  crystalline  form,  and  such  substances 
are  called  isomorphous  ;  examples  are  calcium,  magnesium, 
iron,  and  zinc  carbonates. 

21/7  Many  substances,  not  all,  in  crystallizing  from  water 
solution,  contain  water  as  a  constituent,  although  no  evi- 
dence of  this  is  seen  by  simple  inspection  of  the  crystal. 
This  is  termed  water  of  crystallization.  It  can  generally 
be  driven  off  by  heating,  and  the  crystalline  structure  is 
thus  destroyed,  as  you  have  seen  with  copper  sulphate.  In 
some  instances  the  crystal  first  melts  in  its  water  of  crystal- 
lization, as  in  the  case  of  alum.  Substances  from  which  the 
water  has  thus  been  taken  and  substances  which  contain 
no  water  are  said  to  be  dehydrated  or  anhydrous.  Again, 

21/8  some  substances  lose  their  water  of  crystallization  at  the 
ordinary  temperature;  such  are  called  efflorescent;  exam- 
ples, sodium  carbonate  and  sodium  phosphate.  On  the 
other  hand,  some  substances  absorb  water  from  the  atmos- 
phere and  tend  to  liquefy  in  consequence  ;  these  are  de- 
scribed as  deliquescent ;  examples,  zinc  chloride  (see  Exp. 
17/i  b),  calcium  chloride,  and  sodium  hydroxide.  The  term 
hygroscopic  also  is  applied  to  substances  which  thus  absorb 
water,  but  this  does  not  imply  liquefaction.  Thus,  com- 
mon quicklime — that  is,  calcium  oxide — takes  water  abun- 
dantly, but  retains  the  solid  form. 


INTRODUCTION  11 

Heat  of  solution. — Solution,  when   solute   and  solvent  22 
are  of  the  same  temperature  before  mixing,  is  usually,  not 
always,  accompanied  by  reduction  of  temperature.     Thus, 
common  salt  dissolving  in  water  lowers  the  temperature, 
while  sodium  hydroxide  and  hydrochloric  acid  raise  it. 

Melting  point. — The  melting  point  of  a  substance  is  the  23 
temperature  at  which  it  melts,  and  the  freezing  point  is  the 
temperature  at  which  it  solidifies  ;  and,  being  definite  and 
constant  characteristics  of  a  specified  substance,  they  are, 
as  already  suggested,  useful  in  description.  One  would  ex- 
pect the  two  temperatures  to  be  really  identical,  yet  obser- 
vation shows  that  the  liquid  form  is  sometimes  retained 
below  the  melting  point.  This  phenomenon,  called  sur- 
fusion,  may  cause  irregularity  in  the  observation  of  the 
freezing  point.  Your  experiment  gives  illustration  of  one 
method  applicable  in  such  observations.  "With  a  larger 
quantity  of  the  substance,  the  bulb  of  the  thermometer  may 
be  thrust  into  the  liquid,  and  the  latter  be  stirred  during 
the  solidification. 

The  presence  of  substances  in  solution  tends  to  lower  the  23/1 
freezing  point  of  the  solution  as  compared  with  that  of  the 
pure  solvent.     This  phenomenon  will  be  studied  quantita- 
tively in  Chapter  V. 

Boiling  point,  and  circumstances  affecting  it. — The  boiling  24 
point  of  a  substance,  defined  in  the  strictest  sense  for  pur- 
pose of  description,  is  the  maximum  temperature  which  its 
vapor  attains  when  it  is  in  contact  with  the  boiling  liquid 
and  free  to  escape  into  the  atmosphere  ;  or,  in  other  words, 
when  it  has  a  pressure  or  tension  equal  to  that  of  the  sur- 
rounding atmosphere.  If  this  pressure  is  increased  by  con-  24/1 
fining  the  vapor  or  by  rise  in  the  atmospheric  pressure,  then 
the  temperature  of  the  vapor  and  of  the  boiling  liquid 
will  be  higher ;  if  the  pressure  is  decreased  by  removal  of 
the  vapor  or  by  fall  in  the  atmospheric  pressure,  the  tem- 
perature will  be  lower.  For  complete  definition,  therefore, 
the  pressure  of  the  vapor,  as  well  as  the  temperature,  should 


12          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

be  specified,  and  the  normal  atmospheric  pressure  at  the 
sea  level — that  is,  760  millimeters  or  29.92  inches — is 
chosen  as  the  standard  pressure.  The  ordinary  variations 
of  the  atmospheric  pressure,  however,  have  so  small  effect 
on  the  boiling  point  that  the  variation  may  for  many  pur- 
poses be  ignored.  A  change  of  27  millimeters  (or  1.06 
inches)  in  barometric  pressure,  or  of  about  1,000  feet  in 
elevation,  makes  a  difference  of  1°  C.  in  the  boiling  point. 
Thus  water,  boiling  at  100°  C.  at  sea  level,  boils  at  85°  C. 
on  the  top  of  Mont  Blanc. 

The  facts  that  increase  of  pressure  raises  this  temperature,  and 
that  decrease  of  pressure  lowers  the  same,  find  many  practical  appli- 
cations. Thus  in  extracting  gelatine  from  bones,  the  solvent  power  of 
the  water  is  increased  by  boiling  under  pressure  ;  and  in  the  refining 
of  sugar  the  concentration  of  the  sirup  is  greatly  facilitated  by  evap- 
oration under  diminished  pressure. 

The  boiling  point  has  been  defined,  in  accordance  with 
scientific  usage,  as  the  temperature  of  the  vapor.  Yet  the 
term  is  also  used,  even  in  scientific  literature,  to  designate 
the  temperature  of  the  boiling  liquid.  This  is  unfortunate, 
since  it  is  important  to  discriminate  between  the  two,  for 
the  temperature  of  the  liquid  is  often  higher  than  that  of 
the  vapor.  Various  circumstances  cause  this.  Whatever 
24/2  tends  to  hinder  the  formation  and  escape  of  the  bubbles  of 
vapor  tends  to  raise  the  temperature  of  the  liquid  above 
that  of  the  vapor ;  conversely,  whatever  tends  to  facilitate 
the  same,  tends  to  make  the  temperature  of  the  liquid  the 
same  as  that  of  the  vapor.  Thus,  water  boils  more  readily 
in  an  iron  vessel  with  rough  surface  than  in  a  glass  one 
with  smooth  surface.  Indeed,  in  a  glass  vessel,  whose  inner 
surface  has  been  very  thoroughly  cleaned,  water  may  be 
raised  to  a  temperature  considerably  above  100°  C.  In  this 
condition  a  grain  of  sand  or  a  fragment  of  glass  dropped 
in,  or  a  stirring  rod  inserted,  may  cause  sudden  and  violent 
boiling.  This  phenomenon  of  irregular  boiling,  commonly 
called  in  the  laboratory  bumping,  is  often  very  annoying, 


INTRODUCTION  13 

and  various  expedients  are  used  to  prevent  it,  such  as  con- 
stant stirring,  or  fragments  of  broken  glass,  or  pumice,  or 
platinum  foil.  Thus  also  the  presence  of  dissolved  air  or 
other  gas  tends  to  facilitate  boiling.  On  the  other  hand,  24/4 
the  presence  of  non-volatile  substances  in  solution  tends  to 
raise  the  temperature  of  the  boiling  solution  as  compared 
with  that  of  the  pu?e  solvent ;  this  fact  has  important  quan- 
titative relations,  which  will  be  considered  in  Chapter  V. 

5.  Definitions  and  Classifications 

Some  branches  of  chemistry. — It  is  suitable  to  introduce  at 
this  point  some  additional  statements  and  definitions  which 
do  not  call  for  special  experimental  illustration,  although  it 
is  not  to  tie  expected  that  the  full  significance  of  these 
statements  will  be  understood  at  this  stage  of  the  course. 
From  what  has  been  already  presented,  it  may  be  seen  that 
the  subject-matter  of  our  study  has  a  twofold  aspect.  We  26 
may  give  attention  primarily  to  the  description  and  iden- 
tification and  classification  of  definite  chemical  substances, 
and  this  may  be  called  static  chemistry  ;  or,  on  the  other 
hand,  we  may  give  chief  consideration  to  the  changes  of  sub- 
stances as  changes,  and  this  is  the  aim  of  dynamic  chemistry. 
Of  the  first  division  are  the  subjects  qualitative  analysis 
and  quantitative  analysis.  The  former  consists  of  syste- 
matic methods  for  the  identification  and  recognition  of  sub- 
stances ;  the  latter,  of  methods  for  determining  the  quan- 
tities of  substances.  Analysis  is  ultimate  when  it  is  con- 
cerned with  the  qualitative  or  quantitative  determination 
of  elementary  constituents  ;  and  proximate  when  it  is  con- 
cerned with  constituents  other  than  elementary. 

In  dynamic  chemistry  we  have  to  consider  such  subjects 
as  the  factors,  products,  laws,  agency,  energetics,  etc.,  of 
chemical  change.  For  this  last  phrase  the  more  technical 
one,  chemical  reaction  or  interaction,  is  commonly  used. 
The  factors  are  those  substances  in  presence  before  the 


14          ELEMENTARY  PRINCIPLES  OP  CHEMISTRY 

change  takes  place ;  the  products,  those  present  after  the 
change.  The  factors  and  the  products  considered  collect- 
ively may  be  conveniently  designated  as  the  system  under- 
going change. 

27  Elements  and  compounds  defined. — All  substances  may  be 
classified  as  elements  or  as  compounds.     An  elementary  sub- 
stance is  one  from  a  given  weight  of  which  no  other  sub- 
stance has  been  obtained  less  in  weight  than  the  original. 
Examples :  sulphur,  iron,  zinc,  iodine.     A  compound  sub- 
stance is  one  from  a  given  weight  of  which  other  substances 
have  been  obtained,  each  less  in  weight  than  the  original. 
Examples  :   sulphur   dioxide,  iron   sulphide  (Exp.   13/2a), 
zinc  sulphide,  lead  iodide  (Exp.  15/j),  magnesium,  zinc,  and 
lead  oxides  (Exps.  15/2,  15/3,  and  15/4),  lead  nitrate  (Exp. 
16/!),  zinc  nitrate  (Exp.  16/2). 

28  It  is  important  to  distinguish  between  a  chemical  com- 
pound and  a  mechanical  mixture.    The  first  is  homogeneous, 
and  has  properties  of  its  own,  distinct  from  those  of  its 
constituents ;  the  second  is  not  homogeneous,  and  shows 
only  the  properties  of  its  components.     Thus  the  powdered 
zinc  and  sulphur  in  your  experiment  (Exp.  13/j),  before  the 
application  of  heat,  is  a  mechanical  mixture,  showing  only 
the  properties  of  the  zinc  and  of  the  sulphur.     A  micro- 
scope distinguishes  the  different  color  of  the  zinc  and  sul- 
phur particles.     Water,  dissolving  neither,  separates  them 
more  or  less  completely  by  difference  in  specific  gravity. 
Carbon  disulphide  dissolves  the  sulphur  and  leaves  the  zinc, 
while  hydrochloric  acid  dissolves  the  zinc  and  leaves  the 
sulphur.     But  the  product  of  the  chemical  change — that 
is,  the  zinc  sulphide — has  its  own  properties,  distinct  from 
those  of  zinc  and  those  of  sulphur. 

29  It  is  customary  to  divide  the  elements  into  the  metals 
and  those  which  are  not  metals,  that  is,  the  non-metals, 

*and  to  consider  the  two  classes  separately.  This  classifica- 
tion has  largely  lost  its  original  significance  and  impor- 
tance, however,  and  it  is  preferred,  in  this  presentation,  to 


INTRODUCTION  15 

make  the  classification  a  secondary  matter,  and  to  use  the 
term  metal  rather  in  the  ordinary  non-technical  sense,  im- 
plying those  properties  associated  in  familiar  observation 
with  substances  like  iron,  copper,  gold,  and  silver.  But 
special  importance  is  attached  to  the  question  concerning 
each  element  whether  its  combination  with  oxygen  pro- 
duces a  base-forming  or  an  acid-forming  substance.  The 
elementary  substances  in  alphabetical  list  are  given  in  Table 
X,  No.  643.  They  number  seventy-four,  and  to  this  com- 
paratively small  number  of  constituent  substances  all  known 
forms  of  matter  are  reducible. 

Compounds  classified. — Three  groups  of  compounds  may  30 
be  defined  now ;  they  are  important,  although  they  do  not 
by  any  means  include  all  compounds.     These  are  the  adds, 
the  bases,  and  the  salts.     The  adds  are  substances  contain-  30/1 
ing  hydrogen  as  a  constituent,  which  hydrogen  is  replace- 
able by  a  metal,  the  product  being  a  salt.     When  soluble 
in  water,  as  most  of  them  are,  they  are  sour,  change  blue 
litmus  to  red,  combine  with  bases  to  form  salts,  and  in  con- 
centrated form  are  often  very  corrosive.    Examples  :  hydro- 
chloric, nitric,  and  sulphuric  acids.     A  base  is  a  substance  30/2 
containing  oxygen,  often  hydrogen  also,  and  always  a  con- 
stituent other  than  these  two  which  in  the  most  common 
bases  is  a  metal.     When  soluble  in  water,  they  are  generally 
slimy  to  the  touch,  bitter,  corrosive,  change  red  litmus  to 
blue,  and  combine  with  acids  to  form  salts.     Examples: 
ammonium  hydroxide,  sodium  hydroxide,  lime,  that  is,  cal- 
cium oxide,  and  magnesium,  zinc,  and  lead  oxides.     The 
salts  are  substances  formed  either  by  the  replacement  of  30/3 
the  hydrogen  of  an  acid  by  a  metal,  or  by  the  combination 
of  an  acid  and  a  base.     The  peculiar  properties  of  the  acid 
and  the  base  disappear  in  the  salt,  or  are  neutralized,  some- 
times completely,  sometimes  only  in  part.     When  they  are 
neutralized  exactly,  so  that  the  salt  has  no  action  on  lit-  30/4 
mus,  it  is  said  to  be  neutral.     Examples  :  ammonium  chlo- 
ride, copper  sulphate,  zinc  sulphate,  lead  nitrate.     When 


16          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

all  the  replaceable  hydrogen  of  the  acid  is  completely  and 
30/5  exactly  replaced  by  its  equivalent  of  metal,  or  basic  con- 
stituent, the  salt  is  said  to  be  normal.  A  normal  salt  may 
have  neutral,  acid,  or  basic  reaction  on  litmus ;  thus,  ammo- 
nium chloride  is  normal  and  neutral,  alum  is  normal  and 
has  acid  reaction,  sodium  carbonate  is  normal  and  has  basic 
reaction.  When  a  salt  contains  more  than  the  normal 
30/6  equivalent  of  acid,  it  is  said  to  be  an  add  salt ;  such  are 
sodium  acid  carbonate,  and  acid  sulphate.  When  it  con- 
tains more  than  the  normal  equivalent  of  base,  it  is  said  to 
be  a  basic  salt ;  such  is  the  basic  lead  acetate. 

31  Reactions  classified. — Chemical  reactions  may  be  classi- 
fied, in  part  only,  as  analytic,  synthetic,  and  metathetic,  or 
mixed :  analytic,  when  they  change  compounds  into  their 
constituents ;  synthetic,  when  they  change  constituents  into 
compounds;  and  metathetic,  when  they  involve  both  analy- 
sis and  synthesis,  or  the  exchange  of  constituents.     Thus 
the  conversion  of  iron  and  sulphur  into  iron  sulphide  is 
purely  synthetic ;  of  iron  sulphide  into  iron  and  sulphur  is 
analytic ;  while  the  action  of  hydrochloric  acid  on  iron  sul- 
phide is  metathetic,  since  the  hydrogen  and  the  chlorine  of 
the  first  and  the  iron  and  the  sulphur  of  the  second  are 
separated,  and  then  the  hydrogen  and  the  sulphur  combine, 
also  the  iron  and  the  chlorine.     When  a  constituent  of  a 
compound  is  caused  to   leave   it,  and   another   substance 
appears  as  constituent  in  its  stead,  the  process  is  called 
substitution  (see  Exps.  17,  etc.). 

32  Conclusion. — The  leading  idea  of  this  chapter  is  the  fact 
.    of  chemical  change — that  is,  the  transformation  of  sub- 
stances, involving  the  disappearance  of  some,  and,  depend- 
ent upon  this,  the  appearance  of  others.     This  has  been 
called  change  in  identity.     Along  with  this  have  been  pre- 
sented some  definitions  and  classifications.     And  in  this 
connection  it  is  interesting  and  instructive  again  to  note 
that  the  application  of  these  to  natural  phenontena  is  of£en 
unsuccessful.      Thus  it  seems  a  simple  matter  to  define 


INTRODUCTION  17 

chemical  changes  as  has  been  done ;  nevertheless  changes 
are  not  infrequently  encountered,  of  which  it  is  impossible 
to  decide  whether  they  are  chemical  or  not,  because  it  is 
impossible  to  determine  whether  or  not  there  is  a  distinctly 
new  substance  produced.  So  also  with  regard  to  acids  and 
bases  :  some  substances  act  in  one  compound  as  acid  and 
in  another  as  base,  and  in  some  instances  there  seems  as 
good  reason  to  call  it  the  one  as  the  other.  None  the  less, 
we  may  make  profitable  use  of  such  definitions  and  classifi- 
cations ;  and  at  the  same  time,  we  do  well  to  bear  in  mind 
the  fact  that  nature  is  not  limited  by  the  boundaries  of 
man's  thought. 


CHAPTER  II 

THE   FUNDAMENTAL   QUANTITATIVE  LAWS   OF 
CHEMICAL   CHANGE 

1,   The  Law  of  Persistence  of  Mass 

* 

34  HAYING  now  acquired  a  notion  of  the  method  of  iden- 
tifying and  differentiating  substances,  and  also  of  the  re- 
markable transformations  which  a  system  of  substances 
may  undergo  by  which  other  substances  are  produced, 
differing  entirely  from  the  original  in  properties,  we  pass 
to  a  closer  study  of  the  peculiar  quantitative  character- 
istics of  these  chemical  changes.  And  the  most  funda- 
mental fact  to  be  learned  is,  that  by  these  changes  the 
quantity  of  matter — that  is,  the  mass  of  the  system — is 
neither  increased  nor  diminished.  That  this  is  true,  does 
not  by  any  means  appear  upon  the  face  of  things.  Numer- 
ous experiences  of  everyday  occurrence  can  be  cited  which 
would  seem  to  prove  that  the  reverse  is  true.  Thus  in  the 
burning  of  wood,  or  of  coal,  or  of  a  candle,  one  would  con- 
clude from  appearances,  as  people  did  for  many  years,  that 
matter  is  destroyed,  or  its  quantity  diminished.  If  we  drop 
a  piece  of  marble  into  hydrochloric  acid,  the  marble  slowly 
disappears.  On  the  other  hand,  in  seeing  mercury  sulpho- 
cyanate  burn,  one  might  suppose  that  the  quantity  of  mat- 
ter is  largely  increased.  If,  howeVer,  it  is  burned  on  the 

34/1  balance,  we  see  at  once  that  the  first  supposition  is  wrong ; 
that,  although  it  has  increased  much  in  volume,  the  residue 
which  is  left  on  the  balance  after  burning  actually  weighs 
less  than  the  original  material ;  and,  if  we  burn  a  weighed 

34/2  taper  and  collect  and  weigh  the  products  of  combustion, 
18 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       19 

we  find  that  the  products  weigh  more  than  the  taper  con- 
sumed. Likewise,  if  we  weigh  the  lump  of  marble  and  the  34/5 
acid  before  bringing  them  together  and  afterward,  we 
learn  that  loss  of  weight  accompanies  the  disappearance  of 
the  marble.  What  is  the  explanation  of  these  apparent 
contradictions  ? 

To  answer  this  question  we  must  investigate  still  further 
beyond  appearances.  We  note  that  the  disappearance  of 
the  marble  is  also  accompanied  by  effervescence.  This  im- 
plies the  liberation  of  a  gas,  the  escape  of  which  must  cause 
loss  in  weight.  We  operate  so  as  to  retain  the  gas,  and  we 
rfind  neither  loss  nor  gain  in  weight.  Likewise  we  may 
learn  that  when  the  mercury  sulphocyanate  and  the  taper 
burn,  there  is  combination  of  the  oxygen  of  the  air,  an 
invisible  gas,  with  the  material  of  the  combustible ;  and 
that  other  gases  are  produced,  also  invisible,  which  by 
escaping  cause  loss  of  weight ;  and,  furthermore,  that  these 
gaseous  products,  in  the  case  of  the  taper,  weigh  more  than 
the  taper  consumed  by  just  the  weight  of  the  oxygen  which 
has  entered  into  combination.  The  error  of  the  earlier 
conclusions,  therefore,  has  come  from  overlooking  some 
of  the  substances  involved  in  the  change.  It  is  only 
by  taking  them  all  into  account  that  the  truth  has  been 
reached. 

This  great  law  is  known  as  The  Indestructibility  of  Mat-  34/6 
ter,  or,  better,  as  The  Persistence  *  or  Conservation  of  Mass. 
It  may  be  stated  as  follows  : 

In  any  system  of  substances  undergoing  chemical  change 
the  mass  of  the  entire  system  remains  constant,  or  the 
total  mass  of  the  factors  is  equal  to  the  total  mass  of  the 
products. 

This  law  is  found  to  hold  true  throughout  the  whole  34/7 
range  of  experience,  absolutely  without  exception ;  but  that 

*  "  Persistence"  is  preferred  to  "Conservation,"  following  the  sug- 
gestion of  Herbert  Spencer  in  "  First  Principles." 


20          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

it  is  based  solely  on  experimental  observation,  and  is  not  by 
any  means  axiomatic,  should  not  be  forgotten. 

34/8  It  was  not  discovered  until  the  balance  was  used  to  give 
its  evidence.  And  this  was  done  in  the  main  by  Lavoisier, 
a  French  chemist,  in  a  series  of  investigations,  extending 
from  1770  to  1780,  which  showed  the  error  of  previous  con- 
ceptions, and  which  are  regarded  as  the  beginning  of  modern 
chemistry. 

34/9  This  law  has  its  parallel  in  that  other  great  generaliza- 
tion of  more  recent  discovery,  which  lies  at  the  founda- 
tion of  physical  science,  viz. :  The  Law  of  the  Conserva- 
tion or  Persistence  of  Energy,  which  is  that  in  any  system^ 
of  bodies,  mutually  interacting,  the  total  energy  of  the 
system  remains  constant. 

•   £       2.  The  Law  of  Fixed  or  Definite  Proportions 

37  Analysis  of  your  experiment  with  ammonium  hydroxide 
and  hydrochloric  acid  (No.  37)  shows,  within  the  limit  of 
accuracy  attainable  in  the  given  conditions,  that  the  masses 
.of  these  two  substances  which  combine  to  form  the  salt, 
ammonium  chloride,  bear  a  ratio  to  each  other  which  is 
constant  in  the  three  parts  of  the  experiment ;  that  an  ex- 
cess of  either  constituent  above  this  ratio  has  no  effect 
upon  the  quantity  of  salt  ^btained  nor  upon  its  properties. 
In  other  words,  the  three  portions  of  salt  obtained  are  dif- 
ferent samples  of  the  same  definite  substance  and  contain 
the  same  relative,  quantities  of  the  constituents,  ammonium 
hydroxide  and  hydrochloric  acid. 

37/4  The  fact  here  illustrated  is  found  to  be  a  general  one, 
and  to  bear  the  test  of  the  most  refined  experimental 
methods  without  established  exception.  It  is  formulated 
in  The  Law  of  Fixed  Proportions,  which  may  be  thus  stated : 

3  7/5  Any  sample  of  a  definite  chemical  substance,  not  elementary, 
is  composed  of  the  same  constituents,  combined  in  the  same 
relative  quantities,  as  any  other  sample  of  the  same  substance. 


ANTOINE  LAUBENT  LAVOISIEK 

B.  Paris,  1743.     D.  on  the  scaffold,  1794. 

(See  Nos.  34/8,  235,  259,  306,  388.) 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       21 

The  conception  of  the  fixity  of  ratios  was  in  the  minds  37/6 
of  chemists  more  than  one  hundred  years  ago.  Bergmann 
was  apparently  guided  by  it,  and  Lavoisier  distinctly  for- 
mulated it,  but  its  truth  was  not  admitted  without  dispute. 
It  was  called  in  question  in  1799  by  Berthollet,  a  famous 
French  chemist.  This  led  to  a  long  discussion,  one  of  the 
most  remarkable  in  the  history  of  the  science,  between  him , 
and  another  French  chemist,  named  Proust,  who  undertook 
the  defense  of  the  law.  The  ideas  of  the  latter  prevailed, 
and,  by  1806,  the  truth  of  the  proposition  was  generally 
admitted ;  although  even  in  late  years  there  have  appeared 
suggestions  that  the  law  may  be  subject  to  variations  within 
very  narrow  limits.  In  view  of  this  history  and  of  the 
nature  of  the  law  itself,  the  same  degree  of  absoluteness 
should  not  be  claimed  for  it  as  for  the  first  law. 

It  is  to  be  noted  that  the  Law  of  Fixed  Proportions  37/7 
affirms  the  intimate  relation  between  properties  and  com- 
position. With  identity  of  properties  there  is  identity  of 
composition.  It  does  not,  however,  follow  from  this,  nor  is 
it  indeed  true,  that  with  identity  of  composition  there  is 
identity  of  properties.  There  are  many  substances  not 
identical,  which  are  nevertheless  composed  of  the  same 
constituents  combined  in  the  same  quantitative  ratio. 

To  the   Law  of   Fixed   Proportions  may  be  given  an  37/8 
Alternative  Statement,  somewhat  broader  and  more  suggest- 
ive of  the  dynamic  conception,  thus : 

In  any  system  of  substances  undergoing  chemical  change, 
the  active  masses— that  is,  the  quantities  actually  talcing  part 
in  the  change,  both  of  factors  and  of  products— hear  a  fixed 
ratio  to  each  other,  always  the  same  for  a  specified  change. 

3.  The  Law  of  Multiple  Proportions 

The  third  characteristic  of  chemical  change  is  perhaps  4-0 
even  more  striking  than  the  two  already  studied,  and  is  of 
very  great  significance.     It  was  noted  by  Proust,  and  still 


22          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

earlier  by  Richter,  that  some  substances  combine  in  more 
than  one  ratio,  producing  distinctly  different  substances. 
They  failed,  however,  to  note  the  multiple  relation  of  the 
varying  quantities.  This  was  due,  perhaps,  in  part  to  the 
inaccuracy  of  their  quantitative  determinations.  It  was 
left  to  Dalton,  a  teacher  and  chemist  living  in  Manchester, 
,  England,  to  discover  this  important  relation  and  to  an- 
nounce it  about  the  year  1804. 

The  law  is  illustrated  in  your  experiments  with  mercury 
and  iodine  (Exps.  40,  etc.),  wherein  it  is  seen  that  these 
substances  combine  in  two  different  ratios,  producing  two 
distinctly  different  substances,  and  that  for  the  same  weight 
of  mercury  the  weight  of  iodine  in  one  is  just  twice  that 
in  the  other. 

The  general  fact  is  known  as  The  Law  of  Multiple  Pro- 
portions, and  may  be  stated  thus : 

If  two  substances  combine  in  more  than  'one  ratio,  form- 
ing distinctly  different  products,  and  if  in  such  cases  the 
quantity  of  one  constituent  is  reckoned  as  constant,  then  the 
varying  quantities  of  the  other  constituent  are  in  the  ratio  of 
small  whole  numbers. 

40/6  It  was  the  discovery  of  this  law,  based,  it  is  true,  on 
very  few  observed  instances,  that  led  Dalton  to  the  inven- 
tion of  the  atomic  theory  in  its  modern  form — a  theory 
which  in  importance  is  second  to  none  in  the  science  of 
chemistry. 

40/7  NOTE. — The  law  holds  without  exception,  although  there 
are  many  instances  in  the  so-called  organic  substances,  com- 
pounds of  carbon  with  other  elements,  in  which  the  rela- 
tion seems  less  simple  than  is  stated  in  the  law,  but  they 
do  not  constitute  valid  exceptions  to  the  law  for  reasons 
which  would  hardly  be  understood  at  this  stage  of  the 
course. 

40/8  The  multiple  relation  holds  for  quantities  measured  by 
volume  as  well  as  by  weight,  if  the  substances  are  in  the 
gaseous  condition. 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       23 


4.  The  Law  of  Equivalent  Proportions  * 

It  has  been  seen  in  your  experiments,  Nos.  41/!  and  41/2 ,  41 
that  24  grams  of  magnesium  and  65  grams  of  zinc  combine 
respectively  with  16  grams  of  oxygen  approximately.  De- 
fined with  the  utmost  accuracy,  the  statement  is  that  24.1 
grams  of  magnesium  and  64.91  grams  of  zinc  combine  re- 
spectively with  15.88  grams  of  oxygen.  It  is  also  a  fact, 
although  not  shown  in  your  experiments,  that  these  same 
masses  of  magnesium  and  zinc  combine  respectively  with 
equal  quantities  of  chlorine,  namely,  (2  X  35.18)  grams, 
and  with  equal  quantities  of  iodine,  namely,  (2  X  125.89) 
grams. 

Then  in  your  experiments,  Nos.  41/3  and  41/4 ,  it  is  seen 
that  these  masses  likewise  displace  equal  quantities  of  hy- 
drogen from  an  acid.  This  value,  most  accurately  deter- 
mined, is  2  grams.  Now,  magnesium  and  zinc  do  not  com- 
bine with  each  other,  but  2  grams  of  hydrogen  exactly 
combine  with  15.88  grams  of  oxygen  in  the  formation 
of  water ;  and  one  gram  of  hydrogen  combines  exactly 
with  35.18  grams  of  chlorine,  and  with  125.89  grams  of 
iodine. 

Still  another  phase  of  this  phenomenon  is  seen  in  the  41/6 
following  facts  :  31.83  grams  of  sulphur  combine  with  64.91 
grams  of  zinc  ;  also,  15.88  grams  of  oxygen  with  64.91  grams 
of  zinc ;  and  sulphur  and  oxygen  combine  with  each  other 
in  the  ratio  of  31.83 :  (2X15.88)  in  sulphur  dioxide  and 
31.83  :  (3x15.88)  in  sulphur  trioxide. 

Generalization  upon  the  many  facts  of  this  nature  gives 

*  Inasmuch  as  the  experimental  study  of  this  law  involves  the 
measurement  of  gas-volume,  the  instructor  may  prefer  to  introduce  * 
the  laws  of  Boyle  and  of  Charles,  Chapter  IV,  at  this  point.  The 
writer  prefers  to  give  them  simply  as  arbitrary  rules  and  to  study 
them  later,  rather  than  to  interrupt  the  logical  development  of  this 
chapter. 


24          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

41/7  The  Law  of  Equivalent  Proportions,  to  which  there  seems 
to  be  no  exception ;  it  may  be  stated  thus  : 

The  masses  of  two  or  more  substances,  A,B,C,  etc.,  which 
combine  respectively  with  a  constant  mass  of  another  sub- 
stance, M,  are  also  the  masses  or  bear  the  relation  of  small 
multiples  to  the  masses  of  A,  B,  C,  etc.,  which  may  combine 
respectively  with  a  constant  mass  of  any  other  substance,  X, 
or  which  may  be  chemically  substituted  respectively  for  a 
constant  mass  of  a  substance,  X,  or  which  may  combine  with 
each  other. 

We  may  conceive  that  the  masses  of  two  substances,  A 
and  B,  produce  equal  chemical  effect  when  they  combine 
respectively  with  a  constant  mass  of  the  substance,  X  ;  like- 
wise when  they  displace  a  constant  mass  of  the  constituent, 
C,  from  the  compound,  C  D ;  also  when  they  combine  with 
each  other  to  form  the  compound,  A  B.  By  means  of  this 
conception  the  law  may  be  given  a  more  general  expression 

41/8  in  An  Alternative  Statement,  thus  : 

Those  active  masses  of  substances  which  produce  equal 
chemical  effect  in  a  given  reaction  are  also  the  active  masses 
or  bear  the  relation  of  small  multiples  to  the  active  masses  of 
the  same  substances  which  produce  equal  effect  in  any  other 
reaction  in  which  they  take  part. 

41/9  The  first  notion  of  the  remarkable  facts  generalized  in 
the  fourth  law,  without  by  any  means  a  conception  of 
their  full  extent  or  of  their  significance,  is  credited  by  some 
to  a  German  chemist,  Eichter,  and  to  the  year  1792,  and  by 
others  to  Wenzel,  and  the  earlier  date,  1777. 

Corollaries. — The  following  important  corollaries  are  de- 
ducible  from  the  fourth  law,  taken  in  connection  with 
those  which  precede : 

42  COROLLARY  I. — It  is  possible  to  determine  by  experiment 
what  mass  of  every  elementary  substance  combines  with  one 
gram  of  hydrogen  (the  lightest  substance  specifically  and 
chemically)  or  with  that  quantity  of  some  other  substance 
which,  in  its  turn,  combines  with  one  gram  of  hydrogen 


QUANTITATIVE  LAWS  OF 

(practically  7.94  grams  of  oxygen,  or  85.18  grams  of  chlo- 
rine] ;  or,  what  mass  displaces  one  gram  of  hydrogen  from 
some  specified  compound.  And,  moreover,  the  constituent 
masses  of  the  elements  in  any  compound,  and  their  active 
masses  in  any  reaction,  stand  in  the  ratio  of  these  quan- 
tities or  of  multiples  of  the  same  by  a  whole  number. 

Definition. — These  fundamental  quantities,  specified  in  4:3 
Corollary  I,  are  called  the  equivalent  weights  or  equivalent 
masses  of  the  elements.  Now,  many  of  the  elements  com- 
bine with  hydrogen  or  with  oxygen,  or  with  chlorine  in  more 
than  one  ratio.  These  substances  would  have,  therefore, 
two  or  more  values  which  would  answer  the  definition  of 
equivalent  weight.  But  since  the  relation  of  multiples 
holds  between  these  values,  as  expressed  in  Law  3,  the  fact 
that  there  may  be  more  than  one  value  does  not  interfere 
with  the  truth  of  Corollary  I. 

Great  significance,  both  practical  and  theoretic,  attaches  44 
to  the  equivalent  weights  and  to  the  facts  formulated  in 
this  corollary.  And  the  whole  system  of  expressing  mass 
relations  in  chemical  phenomena  is  based  upon  the  use  of 
the  equivalent  weight,  or  of  a  multiple  of  the  same,  as  a 
chemical  unit,  peculiar  to  each  element,  and  upon  the  ex- 
pression of  the  relative  active  mass  in  terms  of  this  unit, 
with  a  coefficient  which  is  always  a  whole  number.  That 
such  a  system  is  possible,  is  clearly  a  consequence  of  the 
foregoing  laws.  That  one  equivalent  rather  than  another 
is  used,  when  two  or  more  are  possible,  or  that  a  multiple 
instead  of  the  equivalent  itself  is  used  as  the  basal  unit,  is 
a  matter  of  choice,  determined  conventionally  by  the  applica- 
tion of  certain  principles  or  of  certain  theories.  For  the 
reasons  which  are  presented  in  detail  in  Chapter  V,  the 
equivalent  weights  of  certain  of  the  elements  have  been 
multiplied  by  a  small  whole  number,  two,  three,  four  or  five, 
and  the  values  thus  obtained  together  with  those  of  the 
equivalent  weights  which  are  left  unmodified,  all  of  them 
determined  with  the  utmost  available  accuracy,  constitute 


26          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

the  elementary  combining  weights,  which  are  made  the  basal 
units,  just  referred  to,  for  expressing  the  quantitative  mass 
relations  in  chemical  phenomena. 

The  elements  with  their  equivalent  weights,  the  factors, 
and  the  combining  weights  are  given  in  Table  XI,  Ko.  644, 
in  natural  order — i.  e.,  in  the  order  of  increasing  combining 
weights. 

45  COKOLLARY  II. — It  is  evident  that  the  combining  mass  of 
a  compound  must  be  the  sum  of  its  elementary  constituent 
combining  masses. 

For  example :  Using  round  numbers  simply,  the  combining  weight 
of  water  is  18  grams,  since  it  contains  hydrogen  and  oxygen  in  the  ratio 
of  2  grams  to  16  grains — that  is,  two  combining  weights  of  the  former 
to  one  combining  weight  of  the  latter  ;  of  ammonia  is  17  grams,  since 
it  contains  nitrogen  and  hydrogen  in  the  ratio  of  14  grams  to  3  grams 
— that  is,  one  combining  weight  to  three  combining  weights ;  of  carbon 
dioxide  is  44  grams,  since  it  contains  carbon  and  oxygen  in  the  ratio  of 
12  to  32 — that  is,  one  combining  weight  to  two  combining  weights. 

46  COKOLLARY  III. — It  is  possible,  therefore,  to  represent  the 
relative  active  masses  of  all  substances,  in  any  reaction  what- 
soever, as  multiples  by  whole  numbers  of  their  respective  com- 
bining masses. 


5.  The  Law  of  Gas- volumetric  Proportions 

47  The  experiments  (No.  47,  etc.)  with  nitrogen  diox- 
ide and  oxygen,  designed  to  illustrate  this  law,  are  only 
partly  satisfactory,  since  the  volume  of  the  product  can 
not  be  measured  in  the  conditions  of  the  experiment, 
the  substance,  nitrogen  tetroxide,  being  soluble  in  wa- 
ter. Additional  illustrations  are  found  in  the  following 
facts  : 

1  gas-vol.  of  hydrogen  and  1  gas-vol.  of  chlorine  (sum  =  2) 
form  2  gas-vols.  of  hydrochloric  acid. 

2  gas-vols.  of  hydrogen  and  1  gas-vol.  of  oxygen  (sum  =  3) 
form  2  gas-vols.  of  water. 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       27 

3  gas-vols.  of  hydrogen  and  1  gas-vol.  of  nitrogen  (sum  =  4) 
form  2  gas-vols.  of  ammonia. 

In  these  is  revealed  the  surprising  but  none  the  less 
unmistakable  fact,  based  solely  on  experimental  obser- 
vation, that  the  gas-volume  of  a  compound  is  not  always 
equal  to  the  sum  of  its  constituent  volumes,  but  may 
be  less. 

Facts  of  this  nature  are  generalized  into  The  Law  of 
Gas-volumetric  Proportions  as  follows  : 

If  the  constituents  are  gaseous  or  volatile  their  combining 
volumes,  as  gases,  are  in  the  ratio  of  small  whole  numbers, 
and  the  sum  of  these  volumes  stands  in  simple  relation  to  the 
volume  of  the  resulting  compound,  if  the  latter  is  gaseous  or 
volatile.  In  general,  the  compound  occupies  two  unit  gas- 
volumes. 

Note  carefully  that  the  law  is  applicable  only  to  gas-  47/5 
volumes ;  no  such  relations  hold  between  combining  volumes 
other  than  gaseous. 

The  accuracy  of  the  law  is  of  course  limited  by  the  ac-  47/6 
curacy  in  the  measurement  of  gas-volumes.  There  has  been 
much  dispute  as  to  the  generality  of  the  rule  that  the  com- 
pound occupies  relatively  two  unit  volumes.  In  several 
instances  its  volume  is  undoubtedly  larger,  but  it  has  been 
proved  with  much  ingenuity  that  these  exceptional  volumes 
are  due  to  the  decomposition  (dissociation)  of  the  com- 
pounds in  the  conditions  of  observation,  so  that  the  observed 
volume  is  really  the  volume  of  a  mixture  of  the  constituents, 
and  not  of  the  compound  solely. 

The  discovery  of  the  law  is  due  mainly  to  Gay-Lussac,  47/7 
who  with  Humboldt  determined  in  1805  the  gas-volumetric 
composition  of  water,  and  subsequently  extended  his  inves- 
tigations to  other  substances.  The  large  significance  of  this 
law  in  the  interpretation  of  chemical  phenomena  was  not 
realized,  however,  until  a  considerably  later  date. 


28          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


TABLE   I 

49  As  aid  to  a  clearer  understanding  of  these  laws,  the  illustrations 
which  have  occurred  in  the  experiments,  and  some  additional  ones,  are 
tabulated  as  follows : 

1  gram  of  hydrogen  (H)  combines  with 

35.2  grams  of  chlorine  (Cl),  forming  36.2  grams  of  hydrochloric 

acid  (HC1). 

79.3  grams  of  bromine  (Br),  forming  80.3  grams  of  hydrobromic 

acid  (HBr). 

125.9  grams  of  iodine  (I),  forming  126.9  grams  of  hydriodic  acid 
(HI). 

2  grams  of  hydrogen  combine  with 

15.9  grams  of  oxygen  (0),  forming  17.9  grams  of  water  (H20). 

31.8  grams  of  sulphur  (S),  forming  33.8  grams  of  hydrosulphuric 

acid  (HaS). 

3  grams  of  hydrogen  combine  with 

13.9  grams  of  nitrogen  (N),  forming  16.9  grams  of  ammonia  (NH8). 

4  grams  of  hydrogen  combine  with 

11.9  grams  of  carbon  (C),  forming  15.9  grams  of  methane  (marsh 
gas)  (CH4). 

13.9  grams  of  nitrogen  (N)  combine  with 

7.94  grams  of  oxygen  (0),  forming  21.8  grams  of  nitrous  oxide 
(nitrogen  monoxide)  (N20). 

15.9  grams  of  oxygen  (0),  forming  29.8  grams  of  nitric  oxide  (ni- 
trogen dioxide)  (NO). 

23.8  grams  of  oxygen  (0),  forming  37.7  grams  of  nitrogen  trioxide 
(N203). 

31.8  grams  of  oxygen  (0),  forming  45.7  grams  of  nitrogen  tetroxide 
(N204). 

39.7  grams  of  oxygen  (0),  forming  53.6  grams  of  nitrogen  pen- 
toxide  (N266). 

198.5  grams  of  mercury  (Hg)  combine  with 

125.9  grams  of  iodine  (I),  forming  324.4  grams  of  mercurous  iodide 

'  (Hgl). 

251.8  grams  of  iodine  (I),  forming  450.3  grams  of  mercuric  iodide 
(Hgla). 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       29 

15.9  grams  of  oxygen  (0)  combine  with 

24.1  grams  of  magnesium  (Mg),  forming  40.0  grams  of  magnesium 

oxide  (MgO). 

55.6  grains  of  iron  (Fe),  forming  71.5  grams  of  ferrous  oxide  (FeO). 
63.1  grams  of  copper  (Cu),  forming  79.0  grams  of  copper  oxide 

(CuO). 

64.9  grams  of  zinc  (Zn),  forming  80.8  grams  of  zinc  oxide  (ZnO). 
198.5  grams  of  mercury  (Hg),  forming  214.4  grams  of  mercuric 

oxide  (HgO). 
205.3  grams  of  lead  (Pb),  forming  221.2  grams  of  lead  oxide  (PbO). 

31.8  grams  of  sulphur  (S)  combine  with 

24.1  grams  of  magnesium  (Mg),  forming  55.9  grains  of  magnesium 

sulphide  (MgS). 
55.6  grams  of  iron  (Fe),  forming  87.4  grams  of  ferrous  sulphide 

(FeS). 
63.1  grams  of  copper  (Cu),  forming  94.9  grams  of  copper  sulphide 

(CuS). 

64.9  grains  of  zinc  (Zn),  forming  96.7  grams  of  zinc  sulphide  (ZnS). 
198.5  grams  of  mercury  (Hg),  forming  230.3  grams  of  mercuric  sul- 
phide (HgS). 

205.3  grams  of  lead  (Pb),  forming  237.1  grams  of  lead  sulphide 
(PbS). 

31.8  grams  of  sulphur  (S)  combine  with 

15.9  x  2  grams  of  oxygen,  forming  63.6  grams  of  sulphur  dioxide 

(SO*). 
15.9  x  3  grams  of  oxygen,  forming  79.5  grams  of  sulphur  trioxide 

(SO.). 

2  grams  of  hydrogen  are  displaced  from  hydrochloric  acid  by 

24.1  grams  of  magnesium,  forming  magnesium  chloride  (MgCla). 

55.6  grams  of  iron,  forming  ferrous  chloride  (FeCl2). 

63.1  grams  of  copper,  forming  cupric  chloride  (CuCla). 

64.9  grams  of  zinc,  forming  zinc  chloride  (ZnCla). 
198.5  grams  of  mercury,  forming  mercuric  chloride  (HgCla). 
205.3  grams  of  lead,  forming  lead  chloride  (PbCla). 

36.2  grams  of  hydrochloric  acid  (HC1)  combine  with 

16.9  grams  of  ammonia  (NH3),  forming  53.1  grams  of  ammonium 
chloride  (NH4C1). 

63.6  grams  of  S02  combine  with 

15.9  grams  of  0,  forming  79.5  grams  of  sulphur  trioxide  (S03). 


30          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

79.5  grams  of  S03  combine  with 

17.9    grams    of  HaO,  forming    97.4   grains    of    sulphuric    acid 
(H2S04). 

59.6  grams  of  NO  combine  with 

31.8  grams    of  0,  forming  91.4  grams   of  nitrogen    tetroxide 

(N204). 

27.8  grams  of  CO  combine  with 

15.9  grams  of  0,  forming  43.7  grams  of  carbon  dioxide  (C0a). 


49/1         In  the  following,  the  volumes  are  gaseous : 

1  liter  of  hydrogen  (H)  combines  with 

1  liter  of  chlorine  (Cl),  forming  2  liters  of  hydrochloric  acid  (HC1). 
1  liter  of  bromine  (Br),  forming  2  liters  of  hydrobromic  acid  (HBr). 
1  liter  of  iodine  (I),  forming  2  liters  of  hydriodic  acid  (HI). 

2  liters  of  hydrogen  combine  with 

1  liter  of  oxygen,  forming  2  liters  of  water  (vapor)  (H20). 

3  liters  of  hydrogen  combine  with 

1  liter  of  nitrogen,  forming  2  liters  of  ammonia  (NH8). 

1  liter  of  sulphur  (vapor)  combines  with 

2  liters  of  oxygen,  forming  2  liters  of  sulphur  dioxide  (S02). 

3  liters  of  oxygen,  forming  2  liters  of  sulphur  trioxide  (S08). 

2  liters  of  nitrogen  combine  with 

1  liter  of  oxygen,  forming  2  liters  of  nitrous  oxide  (N20). 

1  liter  of  nitrogen  combines  with 

1  liter  of  oxygen,  forming  2  liters  of  nitric  oxide  (NO). 

2  liters  of  oxygen,  forming  2  liters  of  nitrogen  peroxide  (N02). 

2  liters  of  sulphur  dioxide  (S02)  combine  with 

1  liter  of  oxygen,  forming  2  liters  of  sulphur  trioxide  (S08). 

4  liters  of  nitric  oxide  (NO)  combine  with 

2  liters  of  oxygen,  forming  2  liters  of  nitrogen  tetroxide  (N204). 

2  liters  of  carbon  monoxide  (CO)  combine  with 

1  liter  of  oxygen,  forming  2  liters  of  carbon  dioxide  (C09). 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE   31 


6.  The  Law  of  Persistence,  or  Conservation  of  Energy, 
applied  to  Chemical  Phenomena 

Heat  Disturbance  in  Chemical  Reactions 

Chemical  changes  are  generally  accompanied  by  changes  50 
in  energy.  You  have  observed  in  your  experiments  several 
instances  in  which  they  have  been  accompanied  by  the 
liberation  of  heat,  sometimes  sufficient  to  raise  the  mass  to 
incandescence — that  is,  to  a  red  or  white  heat,  as  in  the  com- 
binations of  sulphur  with  iron  and  with  zinc ;  sometimes, 
less  noticeable,  as  in  the  action  of  mercury  and  iodine  ;  and 
sometimes,  still  less  marked,  as  in  the  reaction  of  ammonium 
hydroxide  and  hydrochloric  acid,  and  in  the  action  of  the 
latter  on  magnesium  and  on  zinc.  Likewise  the  reaction 
between  nitric  oxide  and  oxygen  liberates  heat,  although, 
in  the  conditions  of  your  experiment,  you  could  not  easily 
observe  it. 

Now,  heat  is  one  of  the  kinds  of  energy,  and  the  im- 
mediate agent  which  causes  chemical  change  is  another 
kind.  Energy  has  been  defined  as  that  which  brings  about 
changes,  or,  in  the  more  common  wording,  it  is  the  power  of 
doing  work.  The  Law  of  the  Persistence  of  Energy  affirms  * 
(compare  34/9,  Part  I)  that,  although  the  various  kinds  of 
energy  may  be  transformed  from  one  kind  into  another,  the 
total  energy  can  not  be  thereby  increased  nor  diminished. 
Inasmuch,  therefore,  as  heat,  not  before  evident,  appears 
when  iron  and  sulphur  become  iron  sulphide,  and  when 
mercury  and  iodine  become  mercuric  iodide,  it  must  be  that 
iron  sulphide  and  mercuric  iodide  as  compared  with  their 
constituents  have  lost  at  least  as  much  energy  as  is  equivalent 
to  the  heat  produced.  The  energy  which  is  lost  is  the 
chemical  energy  or  chemism,  as  it  is  sometimes  called.  It  51 

*  This  law  was  announced  by  J.  A.  Mayer  in  1842,  greatly  developed 
by  Helmholtz  in  1847,  and  experimentally  tested  by  Joule  in  1850. 


32          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

may  be  that  the  chemical  energy  which  is  lost  does  not 
appear  entirely  as  heat ;  nevertheless,  the  quantity  of  heat 
liberated  is  constant  for  a  specified  change  under  specified 
conditions. 

52  Again,  it  follows  from  this  great  law  that,  in  order  to 
reverse  this  change — that  is,  to  produce  from  iron  sulphide 
and  mercuric  iodide,  iron  and  sulphur,  and  mercury  and 
iodine — the  quantity  of  energy  lost  in  the  first  change  must 
be  restored  to  the  system  in  one  form  or  another. 

53  The  quantity  of  heat  liberated  in  the  original  reactions 
is  called  the  heat  of  formation  of  iron  sulphide  and  of  mer- 
curic iodide  from  their  constituents  respectively.     But  heat 
is  not  always  liberated  in  the  formation  of  compounds ;  it  is 
sometimes  absorbed — that  is,  some  substances  have  a  nega- 
tive heat  of  formation  ;  they  possess  more  energy  than  their 
constituents,  and  consequently  liberate  energy  in  decompos- 

54  ing.     Eeactions  which  liberate  heat  and  compounds  whose 
heat  of  formation   is  positive  are  said  to  be  exothermic ; 
those  which  absorb  heat  and  those  which  have  a  negative 
heat  of  formation  are  called  endothermic. 

The  measurement  of  the  heat  liberated  or  absorbed  in 
chemical  changes  becomes  therefore  an  important  item  for 
investigation,  and  many  extremely  interesting  conclusions 
have  been  reached  by  the  study  of  these  phenomena.  The 
possibility  of  such  measurement  for  reactions  which  are,, 
directly  and  quickly  realizable  can  be  easily  -understood ; 
and  the  application  of  a  corollary  of  the  law  of  persistence 
of  energy  makes  it  possible  to  determine  these  thermal 
values  for  reactions  which  can  not  be  brought  about  in  con- 
ditions suitable  for  heat  measurement,  and,  in  some  in- 
stances, for  reactions  which  can  not  be  brought  about  at  all. 

55  This  corollary  as  applied  to  chemical  phenomena  is  known 
as  The  Law  of  Constant  Heat  Summation.     It  was  formulated 
by  Hess  in  1840,  as  follows :  The  quantity  of  heat  liberated 
or  absorbed  by  a  system  of  substances  undergoing  chemical 
change  is  dependent  on  the  initial  and  final  states  of  the  sys- 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       33 

tern,  and  is  not  affected  by  differences  in  the  intermediate 
states  through  which  the  system  may  pass. 

An  illustration  from  the  reactions  which  you  have  studied 
will  make  this  clear :  16.9  grams  of  ammonia  combine  with 
36.2  grams  of  hydrochloric  acid,  forming  53.1  grams  of 
ammonium  chloride,  a  soluble  salt.  Now  let  us  suppose 
that  we  start  with  ammonia  and  hydrochloric  acid  as  gases 
at  the  ordinary  temperature,  and  end  with  the  salt  dissolved 
in  water  at  the  same  temperature.  The  system  may  be 
passed  from  this  initial  state  to  this  final  state  in  two  dif- 
ferent ways  :  the  two  gases  may  be  directly  combined,  form- 
ing the  solid  salt,  and  then  this  may  be  dissolved  in  the 
water ;  or,  the  gases  may  be  separately  dissolved  in  water 
and  the  two  solutions  mixed,  the  salt  being  formed  in  solu- 
tion. The  law  affirms  that  the  heat  disturbance,  in  passing 
from  this  initial  to  this  final  state,  is  the  same,  whichever 
method  of  reaching  the  final  state  is  used.  The  law  is  ex- 
perimentally verified  by^measuring  the  heal  of  solution  of 
16.;9*grams  of  ammonia  gas%(§,400  calories)  and  of  156.2  grams 
of  hydrochloric  acid  gas  (17.300  calories),  and  the  heat  of 
neutralization  of  the  two  sofufions  (1#,300  calories),  and 
summing  these  three  quantities  (=*.  38,000"  calories) ;  also, 
the  heat  of  formation  of  53.1  grams  of  solid  ammonium 
chloride  from  the  two  gases  (42,lJOO  calories)  and  the  heat 
of  solution  of  the  salt  (—^3,900  calories)  and  summing  these 
two  quantities  (=  38,200  calories).  The  two  sums  are  found 
equal  within  the  limits  of  experimental  error. 

Another  method  of  application  is  seen  in  the  determina-  55/1 
tion  of  the  heat  of  formation  of  15.9  grams  of  methane 
from  its  constituents,  namely,  11.9  grams  of  carbon  and 
4  grams  of  hydrogen;  although  these  elements  can  not 
be  made  to  combine  directly  into  this  compound.  Methane 
is  a  combustible  gas ;  15.9  grams  in  burning  produce  43.66 
grams  of  carbon  dioxide  and  35.76  grams  of  water ;  and  the 
heat  liberated  in  this  reaction  is  found  to  be  212,000  calories. 
Furthermore,  11.9  grams  of  carbon  in  burning  alone  liberate 


34 


ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


56 


57 


97,000  calories ;  and  4  grams  of  hydrogen  in  burning  alone 
liberate  136,800  calories.  Now,  starting  with  11.9  grams  of 
carbon  and  4  grams  of  hydrogen,  we  may  burn  them  sepa- 
rately with  the  requisite  quantity  of  oxygen  and  convert 
them  into  43.66  grams  of  carbon  dioxide  and  35.76  grams 
of  water  with  the  liberation  of  97,000  -f  136,800  =  233,800 
calories.  Or,  starting  with  these  same  quantities,  we  may 
conceive  them  converted  into  15.9  grams  of  methane,  the 
formation  heat  of  which,  a,  is  unknown,  and  then  the  latter 
substance  burned  with  the  liberation  of  212,000  calories. 
Now,  by  the  law,  since  the  initial  and  final  states  are  the 
same,  x  -f  212,000  =  233,800 ;  hence  x  =  21,800  calories. 

One  gram  of  hydrogen  in  burning  to  liquid  water  lib- 
erates 34,200  calories,  which  is  more  heat  than  is  liberated 
by  the  combustion  of  an  equal  weight  of  any  other  sub- 
stance. The  bottleful  of  gas  which  you  collected  in  your 
experiments  with  magnesium  and  zinc  weighed  0.2  of  a 
gram.  This,  if  burned,  would  yield  enough  heat  to  raise 
2.7  such  bottlefuls  of  water  1°,  or  to  raise  68  grams  of 
water  (nearly  2.5  ounces)  from  0°  to  100°. 

The  following  are  the  formation  heats  of  some  of  the 
substances  which  have  been  used  in  your  study : 


Water, 

Sulphur  dioxide, 
Carbon  dioxide, 


H20 
S02 
C0a 


Hydrogen  sulphide,     H2S       = 


Mercuric  iodide, 
Mercurous  iodide, 
Magnesium  oxide, 
Zinc  oxide, 


HgI3 
Hgl 
MgO 
ZnO 


68,400  calories 

71,000 

97,000 

2,700 

24,300 

14,200 

143,400 


=        85,800 


Examples  of  negative  formation  heat  are  : 


Chlorine  monoxide,  C120 

Nitrogen  monoxide,  N2O 

Nitrogen  tetroxide,  N2()4 

Nitric  oxide,  NO 

Cyanogen,  (CN)2 

Acetylene,  C2Ha 


—  17,800  calories 

-  18,000       " 

2,600 

-  21,600 

-  65,600       " 

-  47,600 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       35 

Endothermic  substances  often  show  great  readiness  to  58 
react,  and  are  easily  decomposed,  sometimes  explosively  so 
— e.  g.,  chlorine  monoxide  and  acetylene. 

Chemical  energy  and  electricity. — Chemical  energy  may  59 
be  transformed  not  only  into  heat,  but  also  into  electrical 
energy.  You  have  observed  that  heat  is  liberated  by  the 
solution  of  zinc  in  hydrochloric  acid.  Now,  if  a  sheet 
of  zinc  is  partly  immersed  in  a  beaker  of  dilute  acid, 
and  a  sheet  of  copper,  or  a  carbon  plate,  neither  being 
acted  on  by  the  acid,  is  likewise  immersed  in  the  same 
vessel,  but  separated  from  the  zinc,  and  finally,  if  the  ends 


FIG.  1. — The  galvanic  cell — a  zinc  and  a  copper  plate  (Z  and  C) 
immersed  in  dilute  acid. 


not  immersed  be  brought  in  contact  outside  the  liquid, 
or  connected  by  a  metallic  wire,  the  chemical  energy  set 
free  by  the  solution  of  the  zinc  in  the  acid  now  appears, 
at  least  in  part,  not  as  heat  but  as  the  energy  of  the  elec- 
tric current.  This  constitutes  one  form  of  the  galvanic 
battery,  in  all  forms  of  which  the  electrical  energy  is 
duje  to  the  chemical  changes  taking  place  in  the  gener- 
ating cell. 

Indeed,  it  may  be  said  that,  of  all  the  forms  of  energy, 
the  one  which  produces  chemical  change  is  the  most  familiar 
and  the  most  intimately  associated  with  human  activities ; 
at  the  same  time  it  is  perhaps  the  least  understood.  Not 
only  are  all  those  industrial  applications  of  energy  which 
involve  the  use  of  steam  and  fuel  dependent  on  the  energy 
of  combustion,  which  is  purely  a  chemical  change,  but,  in 
4 


36          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

the  animal  organism,  the  heat,  and  the  energy  of  muscle, 
nerve,  and  brain,  are  likewise  derived  from  the  chemical 
changes  which  the  food  and  other  substances  undergo  in 
the  animal  economy.  [See  Ostwald  (Walker),  "General 
Chemistry,"  page  209.] 


CLAUDE  LOUIS  BEKTHOLLET 

B.  Savoy,  1748.     D.  Paris,  1822. 

(See  No.  37/6.) 


CHAPTER  III 

COMBINING   WEIGHTS-NOTATION-EQUATIONS- 
STOICHIOMETRY-NOMENCLATURE 

1.  Combining  Weights 

THE  combining  weights  of  the  elements  have  already  61 
been  defined  (Nos.  43  and  44,  Part  I).  They  are  multiples  of 
the  equivalent  weights  by  a  small  whole  number  (one  to  five). 
These  multiples  may  be  regarded,  for  the  present,  as  con- 
ventionally chosen  in  accordance  with  principles  which  will 
be  explained  in  Chapter  V.  The  relative  active  mass  of  an 
element  as  a  constituent  in  any  compound  and  as  a  factor 
in  any  reaction  is  represented  as  a  multiple  of  the  com- 
bining weight  by  a  whole  number.  That  this  is  possible 
is  simply  a  consequence  of  the  fundamental  quantitative 
laws,  studied  in  the  last  chapter.  The  system  of  com- 
bining weights,  therefore,  constitutes  the  basis  for  the 
quantitative  expression  of  chemical  phenomena.  Later  it 
will  be  seen  that  very  important  theoretical  conceptions 
center  about  these  values. 


2.  Notation 

The  System  of  Chemical  Notation :  62 

(a)  For  the  elements. — This  consists  simply  in  represent- 
ing the  element  by  a  symbol — usually  the  first  letter,  some- 
times accompanied  by  another,  of  its  name ;  quantitatively 
the  symbol  represents  the  combining  mass  of  the  element 
in  grams. 

37 


38          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

(b)  For  compounds. — This  consists  in  representing  the 
compound  by  a  symbol  or  formula  made  up  of  the  symbols 
of  its  elementary  constituents,  these  being  affected  by  inte- 
gral coefficients  such  that  multiplication  of  the  elementary 
combining  weight  by  the  coefficient  shall  give  products 
which -show  the  relative  masses  of  the  respective  elements 
contained  in  the  compound.  The  coefficient  is  written 
below  the  line  and  follows  the  symbol  to  which  it  belongs. 
If  the  coefficient  is  one,  it  is  omitted  altogether.  A  coeffi- 
cient written  on  the  line  affects  the  symbols  which  follow 
it.  Thus  for  hydrochloric  acid  the  formula  is  HC1,  since  it 
contains  hydrogen  and  chlorine  as  elementary  constituents, 
and  contains  these  in  the  ratio  of  one  combining  mass  of 
hydrogen  to  one  combining  mass  of  chlorine — that  is,  1 
gram  to  35.2  grams.  The  formula  of  water  is  H20,  since 
it  contains  2  grams  of  hydrogen  to  15.9  grams  of  oxygen ; 
of  ammonium  chloride  is  NH4C1,  since  it  contains  nitro- 
gen, hydrogen,  and  chlorine  in  masses  proportional  respect- 
ively to  13.9  :  4  :  35.2. 

62/1  It  is  clear  that  the  formulas,  H2C12,  H402,  and  N2H8C12 
would  represent  the  same  relative  quantities  of  the  ele- 
ments as  those  given  above,  and  so  with  any  set  of  coeffi- 
cients which  preserve  the  ratio  of  the  first.  It  is  custom- 
ary to  use  the  simplest  set  of  coefficients,  unless  there  is 
reason  for  using  multiples  of  these.  The  considerations 
which  determine  the  choice  of  these  possible  multiples  are 
presented  in  Chapter  V. 

62/2  The  combining  weight  of  a  compound  becomes  therefore 
the  sum  of  its  elementary  constituent  masses,  as  expressed 
by  its  formula.  It  is  sometimes  called  the  formula  weight. 
In  the  formulas  of  acids  the  H  is  usually  placed  first ; 
in  those  of  bases  and  of  salts  the  symbol  of  the  metal  is 
usually  placed  first;  in  those  of  oxides  the  0  is  usually 
placed  last. 

PROBLEMS.— Calculate  the  relative  quantities  of  the  elementary  con- 
stituents as  expressed  in  the  following  formulas;  also  the  combining 


COMBINING  WEIGHTS  39 

weights  of  the  compounds :  S02,  FeS,  ZnS,  HaS,  FeCl2,  FeCls,  PbCl2, 
CuS04,  [Ala(S04),-K,S04.24H,0],  CaH402,  C2H2,  C6H6. 

Reckon  also  the  grams  of  the  constituents  contained  in  100  grams 
of  the  compounds — that  is,  the  percentage  composition  of  the  latter. 


3.  Equations 

The  chemical  equation  is  an  attempt  to  describe  a  63 
chemical  reaction  qualitatively  and  quantitatively  in  the 
concise  form  of  an  equation ;  in  it,  the  symbols  of  the  fac- 
tors, separated  by  the  sign  +,  are  written  on  the  left,  and 
those  of  the  products,  similarly  separated,  on  the  right  of 
the  sign  of  equality  (=),  which  is  better  interpreted  by  the 
word  become  or  produce  than  by  the  word  equal ;  the  sign  -f- 
is  interpreted  by  and  or  mixed  with.  When  the  symbols  of 
the  substances  brought  together  are  known,  the  first  mem- 
ber is  easily  written ;  in  order  to  write  the  second,  it  must 
be  learned,  originally  of  course  by  observation,  exactly 
what  substances  are  produced  when  the  factors  are  brought 
together ;  but  this  depends  upon  conditions,  as  you  have 
already  had  opportunity  to  observe,  and  of  these  the  equa- 
tion offers  no  means  of  expression.  Thus  the  equation 

Fe  +  S  =  FeS 

means  that  iron  and  sulphur  mixed  become  iron  sulphide, 
but  this  is  not  true  unless  the  mixture  be  heated  consider- 
ably above  the  ordinary  temperature.  Therefore  the  equa- 
tion, even  in  its  qualitative  aspect,  is  defective,  and  only 
expresses  those  substances  which,  under  certain  conditions, 
not  specified,  are  produced  from  the  given  factors.  Yet 
even  thus  limited,  the  equation  is  useful  in  bringing 
quickly  to  the  eye  the  relations  as  to  composition  between 
the  factors  and  the  products. 

But  the  equation  may  be  used  as  a  means  of  express-  63/1 
ing  also  quantitative  relations  by  letting  each  symbol  stand 
for  a  quantity  of  the   substance   named  which   is   equal 
to  the  combining  weight  in  grams,  or  in  other  units  of 


40          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

weight,  and  applying  to  it  the  coefficient  which  is  neces- 
sary to  express  the  relative  quantities  actually  taking  part 
in  the  reaction — the  active  masses,  as  they  have  been 
called.  Thus  the  equation 

Fe  -f  S  =  FeS, 

quantitatively  interpreted,  means  that  iron  and  sulphur 
produce  iron  sulphide  in  the  proportion  of  55.6  grams,  or 
other  parts  by  weight,  of  iron,  to  31.8  of  sulphur,  to  87.4  of 
iron  sulphide.  And  the  equation 

Zn  +  2HC1  =  ZnCl2  +  2H, 

quantitatively  interpreted,  means  that  64.9  grams  of  zinc 
and  (2  X  36.2)  grams  of  hydrochloric  acid  produce  135.3 
grams  of  zinc  chloride  and  2  grams  of  hydrogen.  Clearly, 
then,  before  the  equation  can  be  used  for  quantitative 
expression,  the  facts  as  to  the  relative  quantities  must  be 
ascertained.  This  can  be  done  originally  only  by  observa- 
tion, and  often  involves  much  labor  and  difficulty.  How- 
ever, it  may  be  assumed  that  the  reaction  as  expressed  by 
the  equation  must  be  in  accordance  with  the  fundamental 
laws  of  quantity  just  studied.  Thus  by  Law  1  there  must 
be  represented  on  one  side  of  the  equation  the  same  quan- 
tity of  each  element  as  upon  the  other  side — that  is,  the 
equation  must  "  balance."  Moreover,  it  is  sometimes  pos- 
sible, when  one  has  become  familiar  with  a  good  many 
reactions  of  the  same  kind,  to  surmise  with  some  degree 
of  certainty  what  change  will  take  place  in  given  condi- 
tions. Nevertheless,  the  beginning  student  should  care- 
fully bear  in  mind  that  facts  must  be  established  before 
equations  are  written ;  and  that,  because  an  equation  is 
written,  and  written  in  accordance  with  the  laws  of 
quantity,  it  does  not  follow  that  it  represents  an  actual 
reaction. 

63/2         Again,  the  equation  as  described  expresses  nothing  as 
to  the  energy  changes  which  always  accompany  the  trans- 


COMBINING  WEIGHTS  41 

formations  of  matter.  So  far  as  the  former  consist  of  heat 
changes,  they  are  expressed  by  a  slight  extension  of  the 
ordinary  chemical  equations.  Thus  : 

Mg  +  0  =  MgO  +  143,400  calories 

means  that  24.1  grams  of  magnesium  combine  with  15.88 
grams  of   oxygen,  producing  39.98  grams  of   magnesium 
oxide  and  liberating  143,400  calories  of  heat  energy. 
And  the  equation 

MgO  =  Mg  -j-  0  —  143,400  calories 

means  that  39.98  grams  of  magnesium  oxide,  in  decompos- 
ing into  24.1  grains  of  magnesium  and  15.88  grams  of  oxy- 
gen, absorb  the  equivalent  of  143,400  calories. 


4.  Stoichiometry 

It  will  be  readily  understood  that  when  the  facts  as  to  64 
relative  quantities  or  active  masses  in  a  given  reaction  are 
known,  they  may  be  applied,  under  the  quantitative  laws 
and  by  purely  arithmetical  analysis,  to  ascertain  the  actual 
quantities  involved  in  specified  conditions.  For  example : 
Suppose  the  problem  is  to  calculate  how  much  hydrogen 
would  be  liberated  by  the  action  of  100  grams  of  zinc  on 
hydrochloric  acid.  The  chemical  fact  is  that  it  takes  64.9 
grams  of  zinc  to  liberate  2  grams  of  hydrogen  (see  equa- 
tion in  63/j),  and  that  the  reaction  always  takes  place  in 
this  proportion  by  Law  2 ;  therefore  by  arithmetical  analy- 
sis the  proportion,  64j) :  JJ  : :  10.0  :  #  gives  the  desired  result. 
Such  chemical  facts  will  be  most  easily  recalled,  probably, 
in  equation  form ;  hence  in  solving  problems  of  this  kind  04/1 
it  is  well  first  to  write  the  equation  for  the  reaction  in- 
volved, then  to  give  to  this  its  quantitative  interpretation 
and  apply  simple  arithmetic.  Calculation  of  this  kind, 
based  on  the  quantitative  relations  of  reactions,  is  called 
Stoichiometry  or  Chemical  Arithmetic. 


4:2          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


5.  Nomenclature 

65  Chemical  nomenclature  is  not  thoroughly  systematic. 
Some  names,  so  far  as  compounds  are  concerned,  give,  with 
more  or  less  system,  some  indication  as  to  the  composition 
and  the  relations  of  the  substances ;  others  have  been  arbi- 
trarily assigned,  perhaps  before  the  chemical  nature  of  the 
substances  was  known.  Only  a  few  general  statements  are 
here  given ;  the  rest  may  come  gradually  as  acquaintance 
with  substances  is  extended. 

65/1  The  elements  in  general  combine  with  oxygen,  and  the 
resulting  compounds  are  termed  oxides  (spelled  also  oxids). 
Examples :  hydrogen  oxide  (commonly  called  water),  zinc 
oxide,  iron  oxide,  sulphur  oxide. 

The  ending  ide  (id)  is  generally  applied  to  the  name  of 
one  of  the  constituents  in  a  compound  which  contains  but 
two ;  thus,  carbides,  nitrides,  and  phosphides  contain  respect- 
ively carbon,  nitrogen,  and  phosphorus,  with  another  ele- 
ment ;  sulphides,  chlorides,  bromides,  and  iodides  contain  sul- 
phur, chlorine,  bromine,  and  iodine  with  another  element. 

65/2  When  there  is  more  than  one  compound  containing  the 
same  constituents  they  are  distinguished  sometimes  by  the 
endings  ous  and  'ic,  as  mercurous  iodide  (Hgl),  in  which 
the  mercury  shows  its  lower  combining  power,  and  mer- 
curic iodide  (HgI2),  in  which  it  shows  its  higher  combining 
power ;  and  sometimes  by  numerals  as  prefixes,  as  in  carbon 
monoxide  (CO)  and  carbon  dioxide  (C02). 

65/8  Names  of  acids. — Acids  containing  no  oxygen  are  given 
the  prefix  hydro  and  the  ending  ic.  Examples  :  hydro- 
chloric, HC1,  and  hydrosulphuric,  H2S.  Other  peculiarities 
are  illustrated  in  the  following  series : 

Hypochlowus  acid HC10 

Chlorous  acid HC102 

Chloric  acid HC103 

Perchloric  acid . .  HC104. 


COMBINING  WEIGHTS  43 

of  salts. — The  salts  of  acids  which  contain  no   65/4 
oxygen  are  named  by  dropping  the  prefix  hydro  of  the  acid 
and  changing  the  ending  ic  to  ide(or  id).     Examples  :  zinc 
chloride,  iron  sulphide. 

The  ending  ic  in  the  names  of  acids  which  contain 
oxygen  is  changed  to  ate  in  naming  their  salts;  and  the 
ending  ous  in  the  acid  to  ite  in  the  salt.  Thus  the  so- 
dium salts  of  the  acid  series  above  mentioned  are  named 
respectively  sodium  hypochlonYe,  chlonYe,  chlom^e,  and 
perchlorate. 

Names  of  bases. — Bases   which   contain  hydrogen   and  65/5 
oxygen  and  another  constituent  (usually  a  metal)  are  now 
commonly  named  hydroxides  (or  ids),  although  they  were 
formerly,  and  by  some  are  still,  called  hydrates.    Examples : 
sodium  hydroxide,  NaOH ;  ammonium  hydroxide, 
and  zinc  hydroxide,  Zn  (OH)8. 


STOICHIOMETRIC   PROBLEMS 

1.  How  much    sulphur  will   exactly  combine   with  75  grams  of   65/6 
iron? 

2.  How  much  zinc  with  50  grams  of  sulphur? 

3.  How  much  zinc  is  needed  to  make  50  grams  of   zinc  chloride 
(ZnCl2)  ? 

4.  How  much  marble  (CaCOs)  must  be  used  with  hydrochloric  acid 
to  generate  enough  carbon  dioxide  (C02)  to  neutralize   50  grams  of 
sodium  hydroxide  (NaOH),  forming  sodium  carbonate  (Na2C03)  f 

5.  How  much  mercury  must  be  added  to  90  grams  of  mercuric  iodide 
(HgI2)  to  convert  it  into  mercurous  iodide  (Hgl)? 

6.  What  volumes  of  carbon  monoxide  (CO)  and  of  oxygen  must  be 
taken  to  produce  by  combination  enough  carbon  dioxide  (C02)  to  neu- 
tralize 10  grams  of  sodium  hydroxide  ?    One  liter  of  oxygen  weighs  1.43 
grams:  one  liter  of  carbon  monoxide  weighs  1.25  grams. 

7.  How  much  magnesium  is  needed  to  generate  with  hydrochloric 
acid  enough  hydrogen  to  form  by  burning  10  grams  of  water! 

S.  Given  :  a  sample  of  hydrogen  containing  nitrogen  as  impurity, 
and  a  sample  of  oxygen  also  containing  nitrogen  as  impurity;  to  de- 
termine the  percentage  of  impurity  in  each  case.  Measured  volumes 
are  caused  to  combine,  forming  water,  liquid  at  ordinary  temperature, 


ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


and  the  following  observations  are  made,  from  which  calculate  the 
impurity : 


RV  taken  =  1  vol. 

Hydrogen  taken  —  2  vols.. 


y 

Hydrogen  taken 
Oxygen  taken 

=  10  vols. 
=    5     " 

Residual  vol.  after 
combination,  RV 

=    3  vols. 

RV  taken 
Oxygen  taken 

=    2  vols. 
1  vol. 

R3V 

=    3  vols. 

R3V  =  2.5  vols. 

Hydrogen  taken  =  2        " 


R4V 


=  4.5  vols. 


pressure.      What 


9.  Gas-volume  =  100  c.c.  at  20°,  and  760  mm. 
would  this  volume  become  at  50°,  and  720  mm.! 

10.  Calculate  the  percentage  of  elementary  constituents  in  the  com- 
pound whose  formula  is  C2H60. 

11.  What  is  the  formula  of  the  compound  which  contains  40.00  per 
cent  of   carbon,  6.67   per  cent  of  hydrogen,  and  53.33  per  cent  of 
oxygen  f 


CHAPTER   IV 

RELATION   BETWEEN   VOLUME,   PRESSURE,   AND 
TEMPERATURE    OF   GASES 

[THESE  topics  belong  strictly  to  the  subject  of  Physics,  but  inasmuch 
as  all  measurement  of  gas-volume  involves  the  application  of  these  laws, 
a  brief  study  of  them  is  here  presented.  If  the  student  has  already  a 
knowledge  of  them  from  a  previous  course,  this  chapter  may  suitably  be 
passed  by.] 

1.  The  Law  of  Boyle 
Relation  between  Volume  and  Pressure  of  Gases 

In  a  confined  mass  of  gas,  the  temperature  remaining  con-  66 
stant,  the  volume  is  inversely  proportional  to  the  pressure ; 
or,  the  product  of  the  volume  by  the  pressure  is  constant. 

COROLLARY. — Density  is  directly  proportional  to  pressure  66/2 
when  temperature  and  volume  remain  constant,  and  it  is  in- 
versely proportional  to  volume  when  temperature  and  pressure 
remain  constant. 

The  law  was  first  discovered  by  Eobert  Boyle  about  1662.   66/3 
Among  Continental  writers  especially,  it  is  often  designated 
by  the  name  of  Mariotte,  who,  however,  did  not  publish  it 
until  1679. 

2.  The  Law  of  Charles 
Relation  between  Volume  and  Temperature  of  Gases 

The  volume  of  a  mass  of  confined  gas,  the  pressure  remain-  67 
ing  constant,  increases  by  ^  or  0.00867  of  itself  at  0°  for 
each  increase  of  one  degree  in  temperature ;  or  its  pressure 
increases  at  the  same  rate,  the  volume  remaining  constant. 

45 


46          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

67/1  COROLLARY. — The  laws  of  Boyle  and  Charles  may  he  ex- 
pressed in  one  as  follows :  The  product  of  volume  hy  pressure 
is  proportional  to  the  absolute  temperature  (that  is,  the  observed 
temperature  plus  273  degrees). 

67/2  The  law  is  also  designated  sometimes  by  the  name  of 
Gay-Lussac,  and  sometimes  by  that  of  Dalton.  It  was  dis- 
covered by  Charles  about  1787. 

67/3  NOTE  I. — Gaseous  substances  tend  to  depart  appreciably 
from  these  laws  as  they  approach  their  points  of  liquefaction. 

67/4  NOTE  II.  — The  laws  of  Boyle  and  Charles  apply  to  gases 
'  in  general,  independently  of  the  chemical  character  of  the 
substances. 


CHAPTEE   V* 

THE   RELATION   BETWEEN   EQUIVALENT   AND    COMBINING 
WEIGHTS  AND  CERTAIN  SPECIFIC  PROPERTIES 

IN  studying  the  qualitative  side  of  chemical  phenom-  68 
ena,  you  have  been  led  to  see  somewhat  of  the  nature  of 
chemical  change  as  involving  the  disappearance  of  some 
kinds  of  matter,  and  in  their  place  the  appearance  of  differ- 
ent kinds — what  has  been  called  the  change  of  identity  in 
substances.  The  contemplation  of  this  phenomenon  gains 
in  impressiveness  with  the  thought  that  by  mastering  thus 
the  production  of  new  substances  man  perhaps  approaches 
as  near  to  independent  creation  as  is  permitted  to  him 
in  any  form  of  his  material  activities.  Certain  it  is  that 
he  has  made  in  the  laboratory  not  only  many  substances 
which  are  identical  with  the  natural  products,  but  innu- 
merable others  as  well,  which  have  never  been  found  in 
nature. 

But  in  further  studying  these  phenomena,  particularly  69 
their  quantitative  aspect,  you  learn,  in  addition,  the  per- 
fectly definite  conditions  imposed  on  such  changes,  and 
hence  the  limitation  imposed  on  man's  productiveness. 
Thus,  no  new  substances  can  be  made,  save  from  those  which 
contain  the  same  elementary  constituents ;  that  is,  the  con- 
stituent elements  must  be  common  to  both  factors  and 


*  If  the  instructor  prefers  to  introduce  at  this  point  a  part  or  the 
whole  of  Chapter  VIII  before  taking  up  Chapters  V,  VI,  and  VII,  no 
embarrassment  will  be  found  in  so  doing.  The  writer  prefers  the  order 
herein  followed. 

47 


48          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

products,  and  the  change  is  simply  a  change  in  their  dis- 
tribution. Nor  can  any  kind  of  matter  be  produced  with- 
out the  disappearance  of  an  equal  mass  of  some  other  kind 
or  kinds. 

70  Summing  up  the  laws  of  quantity  in  the  definition  of 
the  equivalent  and  the  combining  weights,  and  accepting 
these  for  the  present  as  determined  values,  we  pass  on  to 
study  the   numerical   relation   between   these   values   and 
others  which  measure  very  diverse  properties.     The  first  of 
these  to  be  considered  is  the  specific  gravity  of  substances 
in  the  gaseous  condition. 

1.  The  Law  of  Gay-Lussac 

Relation  between  Equivalent  and  Combining  Weights  of 
Gases,  Elementary  and  Compound,  and  their  Specific 
Gravities 

71  The  specific  gravity  of  a  gas  is  defined  as  the  ratio  be- 
tween the  weights  of  equal  gas-volumes  of  the  substance 
and  of  hydrogen,  at  the  same  temperature  and  pressure. 
This  is  sometimes  conveniently  termed  the  vapor-density 
to  distinguish  it  from  the  specific  gravity  of  the  substance 
while  in  liquid  or  in  solid  condition. 

It  is  experimentally  easier  to  weigh  air  than  hydrogen ; 
therefore  experimental  results  are  often  referred  to  air  as 
the  standard.  Such  values  are  converted  to  the  hydrogen 
standard  by  the  factor  14.40,  which  is  the  specific  gravity 
of  air  referred  to  hydrogen  as  unity. 


In  the  accompanying  Table  II,  A,  No.  93,  are  given  those 
of  the  elements  which  are  gaseous  or  volatile  in  conditions 
which  permit  the  determination  of  their  specific  gravity  as 
gases ;  with  these  are  given  also  their  equivalent  weights, 
their  chosen  combining  weights,  and  their  vapor-densities, 


EQUIVALENT  AND  COMBINING  WEIGHTS  49 

as  experimentally  determined,  hydrogen  being  the  standard. 
Since  the  vapor-density  in  some  cases  varies  greatly  with 
the  temperature  of  determination,  and  in  other  cases  re- 
mains practically  constant  through  a  great  range  of  tem- 
perature, some  data  as  to  temperature  of  determination  are 
given ;  also  the  boiling  points. 

Inspection  of  these  data  shows  that  in  the  first  group  of  72 
elements  the  vapor-density  is  numerically  equal  or  approxi- 
mately equal  to  the  equivalent  weight.  Now,  fluorine, 
chlorine,  bromine,  and  iodine,  let  it  be  recalled  (see  Table 
I,  No.  49.),  combine  with  hydrogen  in  the  gas-volumetric 
ratio  of  1  :  1 ;  and  thallium  combines  with  chlorine  in  the 
same  gas-volumetric  ratio.  It  follows  that  if  the  equiva- 
lent weights  in  these  instances  be  chosen  as  the  combining 
weights,  the  formulas  of  these  compounds — for  example, 
HC1,  HBr,  etc. — may  be  interpreted  as  expressing  the  rela- 
tive constituent  quantities,  measured  by  gas-volume  as  well 
as  by  weight,  since  the  coefficients  of  the  elementary  sym- 
bols give  the  ratio  of  the  gas-volumes. 

In  the  second  group  it  is  seen  that  the  vapor-density  of  73 
oxygen  approximates  very  closely  to  equality  with  twice  the 
equivalent  weight.  If  in  this  case  the  equivalent  weight 
7.94  were  chosen  as  combining  weight,  the  formula  of  water 
would  become  HO,  or  some  multiple  of  this,  x  (HO),  in 
which  the  coefficients,  being  equal,  do  not  give  the  gas- 
volumetric  composition.  If,  however,  the  multiple  of  the 
equivalent  weight  by  two  is  chosen  as  combining  weight, 
the  simple  relation  with  vapor-density  reappears,  and  the 
formula  for  water  becomes  H20,  or  some  multiple,  x  (H20), 
in  which  the  ratio  of  the  coefficients,  2:1,  gives  the  ratio  of 
the  gas-volumes. 

Taking  thus  the  vapor-density  as  a  guide  in  the  choice   74 
of  the  multiple  of  the  equivalent  weight  which  shall  be 
used  as  combining   weight,  leads   clearly  in   the   case  of 
tellurium  to  the  second  multiple,  although  the  approxima- 
tion is  not  so  close  as  in  the  case  of  oxygen.     The  same 


50          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

rule  consistently  applied  to  selenium  and  to  sulphur  would 
indicate  the  third  and  the  seventh  multiples  respectively 
instead  of  the  second.  These  two  substances,  sulphur 
especially,  show  a  remarkable  variation  in  vapor-density 
with  temperature,  and  it  is  to  be  noted  that  the  lowest 
values  approximate  closely  to  the  second  multiple.  How- 
ever, the  decisive  reasons  for  the  choice  of  this  mul- 
tiple must  be  looked  for  in  other  relations  (see  Ko.  87, 
Part  I). 

75  In  the  third  group,  as  to  nitrogen,  if  4.64  be  used  as 
combining  weight,  the  formula  of  ammonia  must  be  NH,  or 
some  multiple,  x  (NH),  which  gives  no  indication  of  the 
gas-volumetric  composition.     But  if  the  multiple  by  three 
(viz.,  1&93)  is  chojsen,  the  simple  relation  to  vapor-density 

NH3,  the  coefficients  W3  fa^J^yjMitiojAF  thej^olumes 
of  nitrogen  and  hydrogen  (see  Table  T,  ivo.  49  )v  But  in 

76  the  cases  of  phosphorus  and  arsenic,  the  sixth  multiple  in- 
stead of  the  third  is  indicated,  while  for  bismuth  the  vapor- 
density  is  nearer  the  second  than  the  third,  and  for  anti- 
mony it  is  midway  between  the  third  and  fourth  multiples. 
In  all  these  exceptional  cases  decisive  reasons  for  choice 

77  must  be  sought  in  other  relations.     The  same  must  be  said 
as  to  the  fourth  group,  in  which  zinc  and  cadmium  and 
mercury  show  vapor-densities  approximately  equal  to  the 
equivalent  weights,  and  sodium  and  potassium  to  one^  half 
the  equivalent  weights.     As  to  the  recently  discovered  ele- 
ments, helium  and  argon,  the  data  are  incomplete. 

78  It  must  be  borne  in  mind  that  the  values  for  vapor- 
density  are  in  most  cases  affected  by  much  greater  uncer- 
tainty than  are  the  equivalent  weights,  since  their  deter- 
mination, especially  at  high   temperatures,  involves  great 
experimental  difficulty.     They  may,  nevertheless,  serve  to 
indicate  the  multiple  to  be  chosen,  and  their  indication,  in 
the  absence  of  reasons  for  different  choice,  is  accepted,  we 
may  say  for  the  present,  conventionally. 


EQUIVALENT  AND  COMBINING   WEIGHTS  51 

It  is  evident  that  to  choose  as  combining  weight  for  ele-  79 
ments  the  multiple  hy  a  whole  number  of  the  equivalent 
weight  which  approximates  most  closely  to  the  vapor-density 
has  the  advantages,  first,  of  correlating  in  a  simple  man- 
ner the  two  numerical  values;  and,  second,  in  many  in- 
stances, of  bringing  into  one  formula  the  expression  of 
the  proportion  by  gas-volume,  if  it  is  known,  as  well  as  by 
weight  of  constituents  in  compounds.  These  reasons  for  80 
choice  of  multiple  receive  additional  weight  from  similar 
reasons  which  are  revealed  in  the  study  of  other  widely 
different  properties  which  will  be  presented  in  subsequent 
sections  of  this  chapter.  -There  are  also  very  important 
considerations,  purely  theoretic  in  nature,  which  lead  to 
the  same  choice.  These  will  be  presented  in  connection 
with  the  atomic  theory  (Chapter  VII).  It  is  proper  to  add 
that  the  reasons  of  theory  have  had  historically  probably 
more  influence,  and  still  carry  in  some  minds  more  weight, 
than  the  reasons  of  convenience  just  set  forth. 

B 

In  Table  II,  B,  No.  94,  are  presented  a  few  data  as  to  the  81 
vapor-density  of  gaseous  or  volatile  compounds  which,  in- 
stead of  being  limited  like  the  elements,  are  almost  innu- 
merable. It  is  seen  that,  with  the  multiples  which  were 
indicated  in  the  preceding  paragraph  as  combining  weights 
for  the  elements,  the  vapor-densities  of  the  compounds  ap- 
proximate equality  uniformly  with  one  half  their  combin- 
ing weights;  whereas,  with  the  equivalent  weights  thus 
used  for  the  elements,  the  vapor-densities  in  the  second 
group  would  approximate  equality  with  the  combining 
weights,  and  in  the  first  group  with  one  half  the  combin- 
ing weights,  and  in  the  third  group  with  one  and  a  half 
times  the  combining  weights.  Therefore  the  use  of  the  82 
multiples  chosen  for  the  elements  has  still  an  additional 
advantage  in  bringing  the  vapor-density,  at  least  of  these 
and  similar  gaseous  compounds,  into  simpler  relation  with 
5 


52          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

the  combining  weights  of  the  same.  And  this  also  gives 
83  basis  for  conventionally  choosing  as  the  combining  weight  of 
any  mgaseous  or  volatile  compound,  even  one  whose  gas-volu- 
metric composition  is  unknown,  that  multiple  of  its  simplest 
combining  weight  which  approximates  most  closely  to  its 
vapor-density  multiplied  by  two. 

84-  Thus  in  the  gas,  methane,  1  gram  of  hydrogen  is  com- 
bined with  2.98  grams,  approximately,  of  carbon ;  but  car- 
bon is  practically  non-volatile,  therefore  the  gas-volumetric 
ratio  is  not  known,  and  the  vapor-density,  at  least,  fur- 
nishes no  reason  to  choose  other  value  than  2.98  for  the 
combining  weight  of  carbon ;  but  the  vapor-density  of  the 
compound  is  8.00 ;  hence  we  may  choose  the  multiple  by  4 
— that  is,  16,  or,  more  accurately,  15.9 — as  the  combining 
weight  of  methane,  and  write  its  formula  C4H4.  Consider- 
ations of  a  different  kind  (see  No.  436,  Part  I)  have  led  to 
the  choice  of  11.9,  the  fourth  multiple,  as  the  combining 
weight  of  carbon,  making  the  formula  for  methane  CH4. 

85  Again,  the   substance,  acetylene,  contains   carbon   and 
hydrogen   in  the  ratio  of  11.9  grams  to  1  gram  ;   hence 
its  simplest  formula  would  be  C4H  (carbon  =  2.98),  or  CH 
(carbon  =  11.9),  and  its  combining  weight  12.9.     But  its 
vapor-density  is  13.2 ;  therefore  25.8  (12.9  X  2)  is  chosen  as 
its  combining  weight,  and   C2H2  is  its  accepted  formula. 

85/1  Another  substance,  benzene, 'likewise  contains  carbon  and 
hydrogen  in  the  ratio  of  11.9  grams  to  1  gram,  but  its 
vapor -density  is  40.  Its  simplest  formula  would  be  CH, 
identical  with  the  simplest  one  for  acetylene ;  but  choos- 
ing, in  accordance  with  this  principle,  the  multiple  by  6, 
gives  the  combining  weight  77.5  and  the  accepted  formula 
C6H6. 

86  In  the  last  two  examples  is  seen  still  another  advantage 
of  the  principle  under  consideration,  in  that  it  brings  about 
a  distinction  in  formula  and  combining  weight  between 
different  substances  of  the  same  composition  (compare  No. 
37/7,  Part  I)-    (Such  substances  are  called  isomers.) 


EQUIVALENT  AND  COMBINING  WEIGHTS  53 

Accepting,  then,  this  conventional  rule  for  the  choice  of  87 
multiple  as  combining  weight  in  the  case  of  compounds 
(it  is  more  general  than  the  corresponding  rule  for  elements) 
we  may  reason  backward  to  certain  maximum  values  for 
the  elements  of  exceptional  vapor-density.  Thus>  the  sub- 
stance hydrogen  sulphide  contains  hydrogen  and  sulphur 
in  the  ratio  of  1  gram  of  the  former  to  15.9  of  the 
latter,  and  its  vapor-density  is  17.2.  This  leads  to  33.8 
grams  as  the  combining  mass,  of  which  the  constituents 
must  be  2  grams  of  hydrogen  and  31.8  grams  of  sulphur. 
Therefore  the  combining  weight  of  sulphur  can  not  be 
more  than  31.8.  Likewise  the  vapor-densities  of  the  hy- 
drogen compounds  of  selenium,  phosphorus,  and  arsenic 
indicate  as  maximum  values  for  the  combining  weights  of 
these  elements  78.4,  30.8,  and  74.44  respectively.  And  the 
vapor-densities  of  the  chlorine  compounds  of  antimony  and 
bismuth  indicate  as  maximum  values  for  these  elements 
119.5  and  206.5. 

Effect  of  temperature. — The  simplicity  of  this  relation  88 
between  vapor-density  and  combining  weight  is  somewhat 
disturbed  by  the  fact  that,  in  the  case  of  some  compounds, 
as  of  some  elements,  the  vapor-density  diminishes  with 
increasing  temperature.  This  seems,  however,  to  reach  a 
limit  after  a  certain  interval  of  temperature.  This  is  espe- 
cially notable  in  the  cases  fcf  iodine,  sulphur,  selenium, 
phosphorus,  and  arsenic  among  the  elements  (see  Table  II, 
A),  and  nitrogen  tetroxide  and  ferric  chloride  among  the 
data  of  Table  II,  B. 

Another  class  of  exceptional  compounds  contains  those  89 
which  are  also  exceptions  to  the  law  of  gas-volumetric  pro- 
portions (see  No.  47/6,  Part  I).     These  are  actually  decom- 
posed at  the  temperature  of  observation. 

Upon  these  facts  and  others  of  the  same  nature  is  based 
the  generalization  often  designated  by  the  name  of  Gay- 
Lussac,  who  published  it  in  1808  (see  also  Law  5,  Chap- 
ter II). 


54          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

The  law  may  be  thus  formulated : 

90/1  CLAUSE  I. — The  specific  gravity  of  an  element  in  gaseous 
condition,  referred  to  hydrogen  as  unity,  approximates  nu- 
merically the  equivalent  weight  *of  the  element,  or  a  multiple 
of  the  same  by  a  small  whole  number  ;  and  it  approximates 
equality  with  the  combining  weight. 

90/2  CLAUSE  II. — The  specific  gravity  of  a  compound  in  gase- 
ous condition  (H  =  1)  approximates  numerical  equality  ivith 
one  half  its  combining  weight. 

The  degree  of  approximation  as  well  as  some  of  the 
exceptions  are  seen  in  the  data  of  the  tables. 
An  alternative  statement  of  the  law  is  this : 

90/3  The  combining  weight  in  grams  of  an  element  occupies, 
when  in  gaseous  condition,  a  volume  approximately  equal  to 
that  of  1  gram  of  hydrogen  at  the  same  temperature  and 
pressure;  and  the  combining  weight  of  a  compound,  the 
volume  of  2  grams  of  hydrogen  in  similar  conditions. 

91  NOTE  I. — The  relation  between  the  combining  weights 
and  the  specific  gravities  of  elements  in  the  liquid  and  in 
the  solid  condition  is  not  so  simple  as  in  the  gaseous  condi- 
tion.    There  is,  undoubtedly,  a  relation,  but  in  the  present 
state  of  the  science  it  can  not  be  satisfactorily  defined.     It 
may  only  be  said  that  it  is  probably  a  periodic  function  of 
the  combining  weights.     (The  explanation  of  this  may  be 
deferred.     See  Nos.  423,  589,  and  590,  Part  I.) 

92  NOTE  II. — The  law  of  vapor-densities  may  be  deduced 
from  the  facts  of  gravimetric  and  gas-volumetric  propor- 
tions ;  for  example,  thus :  Since  2  grams  of  hydrogen  com- 
bine with  16  (using  approximate  values)  of  oxygen  and  form 
18  of  water,  and  since  the  gas-volumetric  ratios  are  2:1:2 
respectively,  it  follows  that  16  grams  of  oxygen  and  9  of 
water  must  occupy  a  volume  equal  to  that  of  one  gram 
of  hydrogen,  which  is  the  relation  formulated  in  the  law  of 
vapor-densities.      Likewise   from  the  facts  of  gravimetric 
proportions  and  of  vapor-densities  may  be  deduced  the  law 
of  gas-volumetric  proportions.     (How  ?) 


EQUIVALENT  AND  COMBINING  WEIGHTS 


55 


TABLE  II,  A.* — The  Law  of  Gay-Lussac 


93 


No. 

1 

8 

NAME. 

Equiva- 
lent 
weight. 

Fac- 
tor. 

Combin- 
ing 
weight. 

Vapor- 
density. 

Tempera- 
ture of  ob- 
servation. 

Boiling  point. 

Hydrogen  . 
Fluorine  .  . 

1.0 
18.91 

1 
1 

1.0 
18.91 

1.0 
18.23 

Degrees. 

Degrees. 

Below-230 
Below  -95 

15 

Chlorine  .  . 

35.18 

1 

35.18 

35.83 

200 

-34 

« 

(i 

M 

M 

23.3 

1560 

32 

Bromine  .  . 

79.34 

1 

79.34 

82.77 

102 

59 

u 

u 

" 

(i 

52.7 

1500 

47 

Iodine  

125.89 

1 

125.89 

127.7 

253 

184 

" 

M 

U 

(i 

63.7 

1500 

68 

Thallium  .  . 

202.6 

1 

202.6 

206.2 

1730 

Red  heat. 

7 
14 

Oxygen  .  .  . 
Sulphur  .  .  . 

7.94 
15.915 

u 

2 

2 

u 

15.88 
31.83 

15.90 
112.0 
31.8 

468 
1100-1719 

-186 
446 

31 

Selenium  .  . 

39.2 

2 

78.4 

111.0 

860 

665 

u 

« 

U 

K 

82.2 

1420 

48 

Tellurium  . 

63.25 

2 

126.5 

130.2 

1390-1439 

1390 

6 
13 

Nitrogen  .  . 

Phosphorus 
«< 

4.643 
10.267 

3 
3 

13.93 

30.8 

H 

13.91 
63.96 

45.58 

313 

1708 

-194 

278 

30 

Arsenic.  .  .  . 

24.8 

3 

74.4 

154.2 

644 

" 

u 

u 

" 

79.5 

1700 

46 

70 

9 

Antimony  . 
Bismuth  .  . 

39.7 

68.83 

3 
3 

119.1 
206.5 

141.5 
146.5 

1640 
1640 

1300 
1640 

Sodium  .  .  . 

22.88 

1 

22.88 

12.7 

f 

742 

16 

Potassium  . 

38.82 

1 

38.82 

18.8 

f 

667 

27 

Zinc  

32.45 

2 

64.90 

34.15 

1400 

930 

43 

Cadmium  . 

55.7 

2 

111.4 

57.0 

1040 

770 

67 
73 

Mercury  .  . 
Helium  .  .  . 

99.25 
f 

2 

198.5 
f 

101.0 
2.0 

446-1730 

358 
Below—  230 

74 

Argon  .... 

f 

... 

! 

19.8 

-187 

*  Data  mostly  according  to  Ramsay,  "  Inorganic  Chemistry.' 


56 


ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


TABLE  II,  B.*—  The  Law  of  Gay-Lussac 


NAME. 

Formula. 

Combining 
weight. 

Vapor-density  x  2. 

Hydrogen  fluoride 

HF 

19  91 

19  99 

"         chloride  

HC1 

36.18 

36.38 

"         bromide 

HBr 

80  34 

78  10 

"         iodide  

HI 

126.89 

128  0 

Thallium  chloride 

T1C1 

237.78 

237.4 

Water 

HaO 

17.88 

17.98 

Hydrogen  sulphide  .  . 

H2S 

33  83 

34  4 

"          ^elenide 

HaSe 

80  4 

80  54 

"         telluride  

H2Te 

128.5 

129.6 

Ammonia 

H8N 

16.93 

17.2 

Phosphorus  hydride 

H8P 

33.8 

33.1 

Arsenic  hydride  

H3As 

77.4 

77.8 

Antimony  chloride.  .  
Bismuth          " 

Cl3Sb 
Cl3Bi 

224.7 
312.0 

224.7 
327.7 

Potassium  iodide  

KI 

164.7 

168.9 

Zinc  chloride                 .  .  . 

ZnCl2 

135.27 

132.8 

Cadmium  bromide  
Mercurous  chloride  

CdBr, 
HgCl 

270.2 
270.1 

267.0 
239.6 

Mercuric  iodide  

HgI2 

450.28 

468.0 

Sulphur  dioxide 

SOa 

63.59 

64.9 

CO 

27.79 

27.96 

"       dioxide             .  .  . 

C03 

43.67 

43.98 

Methane    

CH4 

15.91 

16.0 

Acetylene  

CaHa 

25.82 

26.4 

C6H6 

77.46 

79.78 

Nitric  oxide  

NO 

29.81 

30.0 

Nitrogren  peroxide 

N03 

45.69 

45.  8  at  150° 

"        tetroxide 

N304 

91.38 

76.  Oat    26° 

Ferric  chloride                 . 

FeCl3 

161.1 

155.  5  at  750°-1077° 

«            u 

FeaCl« 

322.2 

308  at  440° 

Data  mostly  according  to  Muir,  "  Principles  of  Chemistry." 


JOHN  DALTON 
B.  England,  1766.     D.  1844. 

(See  Nos.  40,  159.) 


EQUIVALENT  AND  COMBINING   WEIGHTS  57 


2.  The  Law  of  Dulong  and  Petit 

Relation  between  Equivalent  and  Combining  Weights  of 
Elementary  Solids  and  their  Specific  Heats 

In  the  accompanying  Table  III,  A,  No.  105,  are  given  95 
the  specific  heats  of  the  solid  elementary  substances,  together 
with  their  equivalent  weights,  the  factors  which  convert 
the  latter  into  combining  weights,  the  combining  weights 
themselves,  and  the  products  of  specific  heats  by  combining 
weights.  Inspection  shows  a  relation  similar  to  that  in  the 
case  of  vapor-density.  In  some  cases  the  equivalent  weight, 
in  other  cases  a  simple  multiple  of  the  equivalent  weight, 
gives  numerically  with  specific  heat  a  product  which  ap- 
proximates equality  for  all  the  solid  elements.  The  prod- 
ucts average  about  6.2  ±. 

It  is  seen  that  the  approximation  to  constancy,  save  in  a  96 
few  instances,  is  a  remarkably  close  one,  although  the  combin- 
ing weights  range  from  7  to  238,  and  the  values  for  specific 
heat  are  affected  with  considerable  uncertainty.  As  bearing 
on  this,  consideration  must  be  given  to  the  fact  that  specific 
heat  varies  with  the  allotropic  condition  of  the  substances, 
and  with  the  temperature  of  determination.  This  is  made 
evident  in  the  data  of  Table  III,  B.  Diamond,  graphite,  and  97 
charcoal  are  allotropic  forms  of  the  element  carbon,  and  the 
table  shows  how  markedly  the  specific  heats  of  the  three  forms 
differ,  even  at  the  same  temperature  of  determination.  It  also 
shows  that  the  specific  heat  increases  with  the  temperature, 
but  at  a  much  smaller  rate  for  high  than  for  low  temperatures. 

These  peculiarities  appear  especially  in  those  substances  98 
which  give  exceptional  products  like  glucinum,  boron,  car- 
bon, and  silicon.  As  the  specific  heat  tends  to  increase 
with  the  temperature,  but  at  a  rate  notably  diminishing  as 
the  temperature  rises,  it  may  be  surmised  that  at  a  sufficient- 
ly high  temperature  the  approximation  to  constancy  would 
be  fairly  satisfactory. 


58          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

99  Eeasons  similar  to  those  suggested  in  considering  the 
vapor-densities  may  suitably  lead  in  the  case  of  elementary 
solids  to  the  choice  for  combining  weight  of  that  multiple 
of  the  equivalent  weight  which,  when  multiplied  by  the 
specific  heat,  gives  the  product  approximating  most  closely 
to  6.2.  This  brings  the  combining  weight  into  simple 
numerical  relation  with  the  specific  heat. 

100  Attention  was  first  called  to  this  relation  by  Dulong  and 
Petit  in  1819,  and  they  urged  the  choice   of   combining 
weights  in  accordance  with  the  above  suggestion.      This 
involved  some  changes  in  the  values  then  in  use,  and  their 
recommendation  was  not  adopted  until  considerably  later. 

The  law  which  is  generally  designated  by  their  names 
may  be  formulated  thus : 

101  The  specific  heat  multiplied  by  the  combining  weight  gives 
numerically  a  product  which  approximates  a  constant  value, 
viz.,  6.2,  for  all  the  solid  elements. 

Inasmuch  as  this  product  is  the  quantity  of  heat,  meas- 
ured, in  calories  (see  Part  II,  50/i),  necessary  to  raise  by 
one  degree  the  temperature  of  the  quantity  of  the  substance 
equal  to  the  combining  weight  in  grams,  the  law  may  be 
given  this  Alternative  Statement : 

102  Quantities  of  the  elementary  solids  equal  to  their  combin- 
ing weights  in  grams  have  approximately  equal  heat  capacity 
— that  is,  they  take  the  same  quantity  of  heat,  viz.,  6.2 ±  cal- 
ories, to  effect  a  rise  of  one  degree  in  temperature. 

NOTE. — This  relation  does  not  hold  for  liquids  nor  for 


103  COROLLARY. — If  the  specific  heat  of  elements  in  the  free 
state  remains  unchanged  when  they  have  passed  into  combina- 
tion, it  follows  that  the  specific  heat  of  a  compound,  multiplied 
by  its  combining  weight,  and  divided  by  the  number  of  elemen- 
tary combining  masses  ivhich  it  contains,  should  give  numer- 
ically a  value  approximating  6.2±  ;  in  other  words,  the  heat 
capacity  of  a  compound  should  equal  the  sum  of  the  heat 
capacities  of  its  constituents. 


EQUIVALENT  AND  COMBINING  WEIGHTS 


59 


Experiment  shows  this  relation  to  hold  in  many  solid 
compounds  which  are  made  up  of  solid  elements,  and  it  is 
designated  as  the  Law  of  Kopp  and  Neumann.  Thus,  spe-  104 
cine  heat  multiplied  by  combining  weight  gives  a  product 
approximately  12  for  the  sulphides  of  iron  and  zinc,  and 
others  like  them ;  whereas  the  heat  capacity  of  the  sulphur, 
5.7,  plus  that  of  the  metal,  6.2  ±,  is  11.9  ±. 


TABLE  III,  A*— The  Law  of  Dulong  and  Petit 


NAME. 

Equivalent 
weight. 

Factor. 

Combining 
weight. 

Specific 
heat. 

Sp.  H.  x 
comb.  wt. 

Lithium  

6.97 

1 

6.97 

0.9408 

6.6 

Glucinum  

4  5 

2 

9.0 

0  58 

5  2 

Boron    ...       

3  62 

3 

10.86 

0.5      (?) 

5  4 

Carbon  (diamond).  .  .  . 
Sodium  

2.9775 

22.88 

4 
1 

11.91 

22.88 

0.459 
0.2934 

5.5 
6.7 

Magnesium  

12.05 

2 

24.1 

0.250 

6.0 

Aluminium 

8  967 

3 

26  9 

0.225 

6.1 

Silicon  (crvs.) 

7.05 

4 

28.2 

0.203 

5.7 

Phosphorus  (crys.)  .  .  . 
Sulphur  ;  .  . 

10.267 
15.915 

3 
2 

30.8 
31.83 

0.202 
0.178 

6.2 
5.7 

Potassium  • 

38  82 

1 

38.82 

0.166 

6.5 

Calcium 

19  9 

2 

39.7 

0.170 

6.8 

Scandium     ... 

14.6 

3 

43.8 

0.153 

6.7 

Chromium    

17.25 

3 

51.74 

0.100(1) 

5.2 

Manganese 

27  285 

2 

54.57 

0.122 

6.7 

Iron. 

27.80 

2 

55.6 

0.114 

6.3 

Nickel  . 

29.12 

2 

58.24 

0.108 

6.3 

Cobalt  

29.3 

2 

58.6 

0.107 

6.3 

31.56 

2 

63.12 

0.095 

6.0 

Zinc 

32  45 

2 

64.9 

0.0956 

6.2 

Gallium 

23.13 

3 

69.4 

0.079  (?) 

5.5 

Germanium  

17.975 

4 

71.9 

0.0758(?) 

5.5 

Arsenic  (crys  ) 

24  8 

3 

74.4 

0.0822 

6.1 

Selenium      .        

39  2 

2 

78.5 

0.076 

6.0 

Bromine  (solid)   .    ... 

79.34 

1 

79.34 

0.0843 

6.7 

Zirconium 

22  425 

4 

89.7 

0.0666 

6.0 

Molybdenum 

47.6 

2 

95.3 

0.0722 

6.9 

Ruthenium. 

50.45 

2 

100.9 

0.0611 

6.2 

Rhodium  

51.1 

2 

102.2 

0.058 

5.9 

Palladium 

52.8 

2 

105.6 

0  0593 

6  2 

Silver  

107.11 

1 

107.11 

0.057 

6.1 

55.7 

2 

111.4 

0.0567 

6.3 

Indium  .  . 

37.67 

3 

113.0 

0.057 

6.4 

105 


*  Data  mostly  according  to  Muir,  "  Principles  of  Chemistry." 


60 


ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


TABLE  III,  A.* — The  Law  of  Dulong  and  Petit — (Continued) 


NAME. 

Equivalent 
weight. 

Factor. 

Combining 
weight. 

Specific 
heat. 

Sp.  H.  x 
comb.  wt. 

Tin  . 

29  525 

4 

118  1 

0  056 

6.6 

Antimony      

39.7 

3 

119.1 

0.0508 

6.1 

Iodine   

125.89 

1 

125.89 

0.0541 

6.8 

Tellurium 

63.25 

2 

126  5 

0  0474 

6.0 

Lanthanum 

45.8 

3 

137.45 

0  0449 

6.1 

Cerium    .       

34.75 

4 

139.0 

0.0448 

6.2 

Tungsten 

91  5 

2 

183  0 

0  0334 

6.1 

Osmium 

47  375 

4 

189.5 

0.0311 

5.9 

Iridium 

47  925 

4 

191.7 

0.0326 

6.2 

Platinum    

48.35 

4 

193.4 

0.0324 

6.2 

Gold 

195  7 

1 

195.7 

0.0324 

6.3 

Mercury  (solid)  
"         (liquid)  

99.25 

2 

198.5 

0.0319 
0.033 

6.3 

Thallium 

202  6 

1 

202  6 

0.0335 

6.8 

Lead                  

102  68 

2 

205.36 

0.0314 

6.4 

Bismuth    

68.83 

3 

206.5 

0.0308 

6.4 

Thorium 

57  725 

4 

230  9 

0.0276 

6.4 

Uranium 

59.45 

4 

237.8 

0.028 

6.7 

106 


TABLE  III,  B.*—  The  Law  of  Dulong  and  Petit 


NAME. 

Temperature. 

Specific  heat. 

Sp.  H.  xcomb.  wt. 

Carbon,  diamond  

—50° 

0.0635 

0.076 

<«             tt 

+  10° 

0,1128 

1.35 

tt                    tt 

85° 

0.1765 

2.12 

it                   it 

250° 

0.3026 

3.63 

u                   ft 

606° 

0.4408 

5.29 

tt                  it 

985° 

0.4589 

5.51 

Carbon  graphite 

—50° 

0.1138 

1.37 

u                    u 

+  10° 

0.1604 

1.93 

tt                             U 

it                   it 

61° 
201° 

0.1990 
0.2966 

2.39 
3.56 

ft                   tt 

250° 

0.325 

3.88 

tt                   it 

641° 

0.4454 

5.35 

tt                   tt 

Wood  carbon  

978° 
0°-23° 

0.467 
0.1653 

5.60 
1.95 

0°-99° 

0.1935 

2.07 

tt          tt 

0°-223° 

0.2385 

2.84 

Data  mostly  according  to  Muir,  "  Principles  of  Chemistry." 


EQUIVALENT  AND  COMBININ 


3.  The  Law  of  Mitscherlich 

Relation  between  Composition,  and  hence  Combining  Weight, 
and  Specific  —  i.  e.,  Crystalline  Form 

The  law  for  present  purposes  may  be  thus  stated  : 
Substances  which  are  similar  in  composition  sometimes  107 

show  the  same  crystalline  form. 

The  similarity  of  composition  here  referred  to  is  seen  in 

the  following  substances  : 

Calcium  carbonate,  CaC03 
Magnesium  carbonate,  MgC03 
Ferrous  carbonate,  FeC03 
Zinc  carbonate,  ZnC03 

They  all  come  under  the  type  expressed  by  the  general 
formula  MC03,  in  which  M  represents  one  combining  mass 
of  the  metal,  and  they  also  show  the  same  form  of  crystal. 
The  substance,  sodium  carbonate,  Xa2C03,  on  the  other 
hand,  does  not  have  a  composition  similar  to  these,  it  comes 
under  a  different  type  ;  nor  does  it  have  the  same  crystal- 
line form. 

The  significance  of  this  relation  in  its  bearing  on  com-  108 
bining  weight  is  only  of  minor  importance.  Its  application 
may  be  thus  illustrated  :  Suppose  it  has  been  determined 
that  the  equivalent  weight  of  zinc  is  32.5,  but  that  there  is 
question  whether  to  choose  this  or  its  multiple  by  2  as  the 
combining  weight.  With  the  former  value,  the  formula  for 
its  carbonate  would  be  Zn2C03  ;  with  the  latter,  ZnC03. 
Suppose  now  that  it  is  observed  to  crystallize  in  the  same 
form  as  the  carbonates  of  calcium,  magnesium,  and  iron, 
which  have  the  accepted  symbols  above  given;  but  this 
crystalline  form  is  not  like  that  of  sodium  carbonate,  which 
substance  has  the  symbol  Na2C03.  These  facts  would  favor 
the  choice  of  65,  rather  than  32.5,  as  the  combining  weight 
for  zinc. 


62          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

The  law  was  discovered  by  Mitscherlich  and  announced 
in  1819. 

4.  The  Law  of  Raoult  (I) 

Relation  between  Combining  Weights  of  Solutes  and  Specific 
Depressions  of  the  Freezing  Points  in  Specified  Solvent 

(See  Part  I,  No.  21) 

109  Preliminary  statement. — It  has  already  been  observed  and 
noted  (see  Part  I,  23/j)  that  the  presence  of  substances  in 
solution  tends  to  lower  the  freezing  point  of  the  solution  as 
compared  with  that  of  the  pure  solvent. 

110  Law  of  proportionality. — For  the  same  substance  in  the 
same  quantity  of  the  same  solvent,  the  depression  of  the 
freezing  point  is  proportional  to  the  quantity  of  the  sub- 
stance dissolved. 

110/a  The  specific  depression  of  the  freezing  point  of  a  sub- 
stance in  a  specified  solvent  is  the  depression  produced 
by  1  gram  of  the  substance  dissolved  in  100  grams  of  the 
solvent. 

111  The  law  (1882). — CLAUSE  I. — The  specific  depression  of 
the  freezing  point  multiplied  by  the  combining  weight  of  the 
solute,  when  the  latter  is  compound,  gives  a  product  (D) 
which  is  approximately  the  same  for  all  compound  solutes  in 
the  same  solvent,  but  differs  with  different  solvents. 

112  CLAUSE  II. —  When  the  solute  is  elementary,  its  specific 
depression  multiplied  by  its  combining  weight,  or  a  multiple 
of  the  latter  by  a  small  whole  number,  gives  a  product  (D) 
which  is  approximately  the  same  for  all  elementary  solutes 
and  equal  to  that  for  compounds  in  the  same  solvent,  but 
which  differs  ivith  different  solvents. 

113  As  to  data. — The  law  finds  verification  in  many  instances, 
but  it  fails  in  many  others ;  and  the  phenomenon  is  greatly 
complicated  by  the  fact  that  the  law  of  proportionality  does 
not  always  hold  good.     This  throws  doubt  on  the  calcula- 
tion of  the  specific  depression  and  of  the  constant  of  de- 


EQUIVALENT  AND  COMBINING  WEIGHTS  63 

pression,  D.  Proportionality  often  holds  while  solutions  are 
very  dilute,  but  ceases  when  they  become  concentrated.  A 
similar  difficulty  was  noted  in  connection  with  vapor-density 
(see  Nos.  88  and  89,  Part  I)  and  specific  heat  (see  Nos.  97 
and  98),  the  values  for  which  vary  with  the  temperature  of 
determination. 

A  very  slight  illustration  of  this  is  seen  in  the  data  for  114 
sulphur  and  for  iodine  as  solutes,  which  are  given  in  Table 
IV,  C  (No.  122).  The  specific  depression  of  the  former 
varies  from  0.265°  to  0.248°  when  the  concentration  va- 
ries from  2.4  to  7.2  per  cent,  while  that  of  iodine  varies 
from  0.272°  to  0.251°  with  a  variation  in  per  cent  from 
2.2  to  3.7. 

A  great  many  data  for  compounds  in  various  solvents  115 
have  been  accumulated.  To  give  some  idea  of  the  approach 
to  constancy  under  the  law,  a  few  experimental  values  are 
cited  in  Table  IV,  A  and  B  (Nos.  120  and  121).  An  ex- 
planation has  been  offered  for  such  abnormally  high  prod- 
ucts as  are  found  for  the  last  five  substances  in  water  solu- 
tion (No.  121) ;  it  is  based  on  the  assumption  that  there  is 
actual  decomposition  of  these  substances  in  solution  (com- 
pare with  Nos.  47/6,  88,  and  89). 

The  observations  for  elementary  substances  are  few,  116 
since  but  few  of  the  elements  are  soluble  in  ordinary  solvents 
without  chemical  change.  In  Table  IV,  C  (No.  122)  are 
given  the  data  for  the  constant  of  depression  (D)  in  the 
cases  of  phosphorus,  sulphur,  bromine,  and  iodine.  The 
large  factors  for  phosphorus  and  sulphur  should  be  noted 
in  comparison  with  those  relative  to  vapor-density  (see 
Nos.  74  and  76). 

The  constant  of  depression,  D,  for  a  specified  solvent  may  117 
be  determined  by  averaging  the  products  for  a  large  num- 
ber of  substances  of  known  combining  weight,  such  as  are 
exhibited  in  Table  IV,  A  and  B,  for  acetic  acid  and  water 
as  solvents ;  but  it  may  also  be  obtained  by  a  calculation 
based  upon  the  freezing  point  of  the  pure  solvent  and  the 


ELEMENTARY   PRINCIPLES  OF  CHEMISTRY 


latent  heat  of  fusion,  measured  in  calories,  for  100  grams 
of  the  solvent.  The  calculated  and  the  observed  values 
agree  closely  in  many  instances.  A  few  examples  are  given 
in  Table  IV,  D  (No.  123). 

118  An  alternative  statement  of  Eaoult's  law  may  be  made 
as  follows  :  Masses  of  solutes  which  are  proportional  to  their 
combining  weights,  or  in  the  case  of  elements  to  simple  mul- 
tiples thereof,  when  dissolved  in  100  grams  of  the  same  sol- 
vent, produce  approximately  equal  effects  in  depressing  the 
freezing  point  of  the  solutions  as  compared  with  that  of  the 
solvent. 

119  Method  of  applying.  —  Suppose  it   is   questioned  what 
multiple  of  16.9  shall  be  used  as  the  combining  weight 
of  hydrosulphuric  acid.     Experiment   gives   1.05°   as   the 
specific    depression    for    this    substance    in    acetic    acid. 
Hence,  by  Eaoult's  law, 

OQ 

Comb.  wt.  =  -^  =  37±; 

J..UO 

and  the  multiple  of  16.9  by  2  is  chosen,  since  it  approximates 
most  closely  to  37  ± . 

120  TABLE  IV,  K*—Raoults  Law  (I) 

Solvent,  acetic  acid.     Freezing  point  =  16.75°.     Constant,  D  =  39°. 


SOLUTE. 

Formula. 

Product,  D°. 

Alcohol                      

C2H60 

36.4 

Ether  

C4H100 

39.4 

Chloroform       .... 

CC13H 

38.6 

Glycerine          

C8He03 

36.2 

Naphthalene 

39.2 

Camphor                               

Ci0H160 

36.4 

Water    

H20 

33.0 

Carbon  disulphide 

CS2 

38.4 

Hydrosulphuric  acid    .... 

H3S 

35.6 

Sulphur  dioxide 

S02 

38.5 

Sulphuric  acid  

H2S04 

18.6 

Hydrochloric  acid    . 

HC1 

17.2 

Mg(C2H809)3 

18.2 

JEREMIAS  BENJAMIN  RICHTEE 

B.  Germany,  1762.     D.  1807. 

(See  No.  41/9.) 


EQUIVALENT  AND  COMBINING   WEIGHTS 


65 


TABLE  IV,  B.*— Raoulfs  Law  (I) 
Solvent,  water.     Freezing  point,  0°.     D  =  19°. 


121 


SOLUTE. 

Formula. 

Product,  D°. 

Alcohol  

C2H60 

17.3 

Glycerine             .          .             ... 

C3H803 

17.1 

Cane  sugar  

18.5 

C2H4O2 

19.0 

Magnesium  sulphate 

MgS04 

19  2 

Ferrous             "             ... 

FeS04 

18  4 

Zinc                   "           

ZnS04 

18.2 

Copper                         

CuS04 

18.0 

Hydrochloric  acid. 

HC1 

39  1 

Ammonium  chloride 

NH4C1 

34.8 

Potassium           " 

KC1 

33.6 

"          tartrate  

K2C4H406- 

36.3 

Pb(N03)2 

37.4 

TABLE  IV,  C.—Raoulfs  Law  (I) 


122 


Concen- 

SOLUTE. 

Solvent. 

tration. 
Grams  in 
100  of 

Spec.  D. 

Multiple  of 
comb.  wt. 

D° 

(exp.). 

D° 
(cal.). 

solvent. 

Phosphorus  f  . 
Sulphur  f  

Benzene  .... 
Naphthalene. 

0.72 
2.42 

0.392° 
0.265° 

30.8x4 
31.8x8 

48.3 
67.4 

51.0 
69.4 

" 

7.20 

0.248° 

Bromine  \  ,  .  .  . 

Acetic  acid.  . 

1.71 

0.251° 

79.3x2 

39.8 

38.8 

Iodine  \ 

Naphthalene. 

2  19 

0.272° 

125.9x2 

68.5 

69  4 

<* 

3.72 

0.251° 

TABLE  IV,  D.*— Raoulfs  Law  (I) 


123 


SOLVENT. 

D°  observed  average. 

D°  calculated. 

Water 

18.5 

18.9 

Acetic  acid                .       ... 

39.0 

38.8 

Benzene        

49.0 

51.0 

Naphthalene  .  . 

71.0 

69.4 

*  According  to  Ostwald  (Muir),  "  Solutions." 

f  According  to  Hertz,  Zeitschrift  fur  physikalische  Chemie,  VI,  358 
(1890). 

£  According  to  Paterno  and  Nasini,  Berichte  der  deutschen  che- 
mischen  Gesellschaft,  xxi,  2153  (1888). 

*  According  to  Nernst  (Palmer),  "  Theoretic  Chemistry." 


66          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


5.  The  Law  of  Baoult  (II) 

Relation  between  Combining  Weights  of  Solutes  and  Spe- 
cific Elevations  of  the  Boiling  Temperature  in  Specified 
Solvent 

124  Preliminary  statement. — The  facts  presented  in  the  pre- 
ceding section  relative  to  the  freezing  point  of  solutions 
are  closely  paralleled  by  the  facts  relative  to  the  boiling 
temperature  of  the  same.     Attention   has    already  been 
given  to  the  fact  that  the  presence  in  solution  of  iion-vola- 
tile  substances,  or  of  substances  practically  non-volatile  in 
the  actual  conditions  tends  to  raise  the  temperature  of  the 
boiling  solution  as  compared  with  that  of  the  pure  solvent 
(compare  No.  24/4).      This  temperature  is  not  to  be  con- 
fused with   that   of  the   boiling   point,  which  is   strictly 
the   temperature  of  the  vapor,  not  of  the  liquid.      The 
term  "boiling  temperature"  is  herein  used  to  designate 
the  first. 

125  Boiling  takes   place  when  the   pressure   of  the  vapor 
which  is  formed  in  the  body  of  the  liquid  just  exceeds  the 
pressure  of  the  atmosphere  plus  the  resistance  which  the 
liquid  offers  to  the  formation  and  movement  of  bubbles. 
Now,  the  presence  of  non-volatile  substances  in  the  liquid 
reduces  the  vapor-pressure  for  a  given  temperature,  and 
consequently  increases  the  temperature  which  is  necessary 
to  produce  a  vapor-pressure  equal  to  the  opposing  pressure 
of  the  atmosphere ;   in  other  words,  it  raises  the  boiling 
temperature  of  the  liquid,  although  the  temperature  of  the 
vapor,  after  it  has  escaped  from  the  liquid — i.  e.,  the  boiling 
point — may  be  unaffected. 

126  The  law  of  proportionality. — For  the  same  substance  in 
the  same  quantity  of  the  same  solvent  the  elevation  of  the 
boiling  temperature  is  proportional  to  the  quantity  of  the 
substance  dissolved. 

The  specific  elevation  of  the  boiling  temperature  of  a 


EQUIVALENT  AND  COMBINING  WEIGHTS  67 

substance  in  a  specified  solvent  is  the  elevation  produced 
by  1  gram  of  the  substance  dissolved  in  100  grams  of  the 
solvent. 

The  law  (1886).— CLAUSE  I.— The  specific  elevation  of  127 
the  boiling  temperature  multiplied  by  the  combining  weight 
of  the  solute,  when  the  latter  is  compound,  gives  a  product 
(E)  which  is  approximately  the  same  for  all  compound 
solutes  in  the  same  solvent,  but  differs  with  different  sol- 
vents. 

CLAUSE  II. —  When  the  solute  is  elementary,  its  specific  128 
elevation  multiplied  by  its  combining  weight,  or  a  multiple  of 
the  latter  by  a  small  whoU  number,  gives  a  product  (E)  which 
is  approximately  the  same  for  all  elementary  solutes  and  equal 
to  that  for  compounds  in  the  same  solvent,  but  which  differs 
with  different  solvents. 

As  to  data. — The  statement  made  concerning  exceptions  129 
both  to  the  law  of  proportionality  and  to  the  law  of  Kaoult 
relative  to  freezing  point  is  equally  applicable  to  the  phe- 
nomenon of  boiling  temperature.  There  are  many  verifica- 
tions, but  also  many  exceptions.  Variation  from  propor- 
tionality is  seen  in  the  data  for  sulphur,  Table  V,  F.  For  a 
concentration  of  1.5  per  cent  the  multiple  of  the  combining 
weight  by  8  gives  a  good  approximation  to  the  expected 
product ;  whereas  at  a  concentration  of  10  per  cent  the 
factor  9  gives  the  closest  approximation.  A  few  of  the 
very  many  experimental  determinations  for  compounds  are 
given  in  Table  V,  E,  and  those  of  the  available  elements  in 
Table  V,  F. 

The  constant  of  elevation,  E,  for  a  specified  solvent  may  130 
also   be   calculated    from   the    experimentally   determined 
boiling  temperature  of  the  solvent  and  the  latent  heat  of 
vaporization,  measured   in   calories,  for  100  grams  of  the 
same. 

An  alternative  statement  of  this  law  may  be  made  in   131 
terms  exactly  similar  to  those  employed  in  the  law  relative 
to  the  freezing  point  of  solutions. 


68 


ELEMENTARY   PRINCIPLES  OF  CHEMISTRY 


TABLE  V,  E.*— Raoulfs  Law  (II) 
132    Solvent,  alcohol.   Boiling  point =78. 3°.  Constant,  E= 11. 5°  (calculated). 


SOLUTE. 

Formula. 

Comb.  wt. 

Products. 

Concen- 
tration. 

Spec.  E. 

Naphthalene  

Ci0H8 
CN2H40 
C7H602 
HgCl2 
LiCl 
KC2H3Oa 

ing  point,  10( 

128 
60 
122 
271 
42.5 
98 

)°.    Cons 

10.0 
11.1 
12.2 
11.7 
13.2 
12.0 

bant,  E  = 

5.2°  (cal 

culated). 

Urea  

Benzoic  acid  

Mercuric  chloride.  .  . 
Lithium        " 
Potassium  acetate.  .  . 

133   Solvent,  water.    Boil 

Cane  sugar 

Ci2H22Oii 
C6H1406 
CN2H40 
H3B03 
HgCla 
CdI2 
NaC2H30, 

342 
182 
60 
62 
271 
366 
82 

4.9 
5.0 
4.3 
4.8 
5.0 
5.2 
9.6 

Mannite  .  .             .    . 

Urea  

Boric  acid 

Mercuric  chloride.  .  . 
Cadmium  iodide.  .  .  . 
Sodium  acetate.  . 

134   Solvent,  carb.  disulphide.  Boiling  point,  46.2°.  Constant,  E  =  23.7°  (calc.). 


Anthracene 

C14Hio 

178 

24.4 

0.59 

0.137 

« 

23.7 

4.02 

0.132 

Naphthalene  

C10H8 

128 

23.2 

2.99 

0.181 

21.9 

7.54 

0.171 

Camphor 

C,0H,80 

152 

21.4 

2.02 

0.141 

u 

« 

21,1 

8.09 

0.139 

TABLE  V,  F.f—  Raoulfs  Law  (II) 
135    Solvent,  carbon  disulphide,    Boiling  point,  46.2°.    Constant,  E  =  23.7°. 


SOLUTE. 

Concentration. 
Per  cent. 

Spec.  E. 

Multipleof  comb.  wt. 

Product,  E. 

Phosphorus  
u 

Sulphur  

1.58 
10.80 
1.52 
10.00 

0.185° 
0.159° 
0.094° 
0.083° 

30.8x4 
a 

31.8x8 
«c 

-    22.8° 
19.6° 
24.0° 
21.0° 

Iodine    

1.27 

0.095° 

125.9x2 

23.9° 

9.00 

0.087° 

it 

21.9° 

*  According  to  Beckmann,  Zeitschrift  fur  physikalische  Chemie,  vi, 
437  (1890).  t  Ibid.,  v,  76  (1890). 


EQUIVALENT   AND  COMBINING  WEIGHTS  69 

SUMMAET 

In  summing  up  the  facts  presented  in  this  chapter  rela-  136 
tive  to  the  elements,  it  is  seen  that  masses  of  these  sub- 
stances, which  are  proportional  to  their  equivalent  weights 
or  to  products  thereof  by  a  small  whole  number,  produce 
equal,  or  approximately  equal,  effects  in  occupying  volume 
when  in  the  gaseous  condition ;  in  absorbing  heat  with 
equal  changes  of  temperature  when  in  the  solid  condition ; 
and  in  depressing  the  freezing  point  and  raising  the  boiling 
temperature  when  in  dilute  solution  by  equal  quantities  of 
the  same  solvent. 

Moreover,  it  is  learned  that  simplicity  of  relation  is  187 
brought  about  by  choosing  for  combining  weight  the  exact 
multiple  of  the  equivalent  weight  which  in  the  gaseous 
state  occupies  a  volume  most  closely  approximating  that 
occupied  by  1  gram  of  hydrogen  in  similar  conditions  of 
temperature  and  pressure,  and  which  in  the  solid  state 
requires  a  quantity  of  heat  most  closely  approximating 
6.2  ±  calories  to  effect  a  rise  of  one  degree  in  tempera- 
ture; and  that  the  choice  is  conventionally  made  in  ac- 
cordance with  these  principles,  unless  reason  is  found  for 
choosing  otherwise. 

Relative  to  compounds,  it  is  learned  that  masses  of  these  138 
equal  to  their  simplest  combining  weights  in  grams  do 
in  many  instances  occupy  in  gaseous  condition  approxi- 
mately equal  volumes,  and  that  this  volume  is  equal  to  that 
occupied  by  2  grams  of  hydrogen  at  the  same  tempera- 
ture and  pressure.  And  again,  for  simplicity  of  relation, 
that  exact  multiple  'of  the  simplest  possible  combining 
weight  is  conventionally  chosen  for  the  actual  combining 
weight  which  in  the  form  of  gas  occupies  a  volume  most 
closely  approximating  that  of  2  grams  of  hydrogen.  In 
addition,  it  is  learned  that  masses  of  compounds  which  are 
proportional  to  their  combining  weights  likewise  in  many 
instances  produce  equal  effects  in  depressing  the  freezing 


TO          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

point  and  in  elevating  the  boiling  temperature  when  in 
solution  under  similar  conditions. 

139  And,  finally,  in  comparing  elements  with  compounds  it 
is  to  be  particularly  noted  that  the  combining  masses  of 
the  elements  must  generally  be  multiplied  by  a  small  factor 
in  order  to  produce  equal  eifects  with  those  of  the  combin- 
ing masses  of  the  compounds,  in  respect  to   the  specific 
properties  herein  studied.     In  the  matter  of  vapor-density 
(see  Table  II,  Nos.  93  and  94)  the  factor  is  generally  2. 
Exceptions  may  be  noted  as  follows :  for  iodine  the  factor 
is  2  at  low  temperature  and  1  at  high,  but  it  is  2  in  relation 
to  freezing  point  and  boiling  temperature ;  for  sulphur  the 
factor  is  7  at  low  temperature,  2  at  high,  and  8  or  more  in 
relation   to   freezing  point   and  boiling  temperature ;  for 
phosphorus  it  is  4  at  low  temperature  and  the  same  for  the 
phenomena  of  the  freezing  point  and  boiling  temperature ; 
for  arsenic,  relative  to  vapor-density,  it  is  4  at  low  and  2  at 
high  temperature,  while  it  is  1  for  sodium,  potassium,  zinc, 
cadmium,  and  mercury. 

140  Relative  to  specific  heat,  on  the  other  hand,  the  factor 
varies  and  is  equal  to  the  number  of  elementary  combining 
masses  which  the  compound  contains. 

141  Great  significance  is  attached  to  the  facts  of  this  chap- 
ter, and  important  theoretic  conceptions  are  based  upon 
them.     The  correlation  of  these  widely  diverse  phenomena, 
and  there  are  likewise  others  which  have  not  been  here 
presented,  with  those  of  chemical  change  can  not  but  be 
impressive  to  the  thoughtful  student  of  nature.     It  forces 
upon  him  the  conviction  that  there  must  be  some  cause 
underlying  the  common  relation ;  and  men  have  not  been 
slow  in  their  attempts  to  discover  and  explain  this  cause. 
The  outcome  of  their  efforts  will  be  set  forth  in  connection 
with  the  atomic  theory  in  Chapter  VII ;  but,  preceding  this, 
it  is  well  to  give  brief  consideration  to  the  method  of  deter- 
mining experimentally  these  fundamental  values,  the  equiva- 
lent and  combining  weights. 


CHAPTER  VI 

METHOD   OF  DETERMINING   EQUIVALENT  AND  COMBINING 
WEIGHTS  OF  ELEMENTS  AND  FORMULAS  OF  COMPOUNDS 

1.  Determination  of  the  Equivalent  Weight  of  an  Element 

THE  equivalent  weight  of  an  element  has  already  been  142 
defined  (see  Nos.  42  and  43).  The  most  direct  method  of 
determining  its  value  is  to  ascertain  by  experiment  what 
mass  of  the  substance  combines  with  1  gram  of  hydro- 
gen. If  it  combines  in  more  than  one  ratio  with  hydrogen, 
under  the  law  of  multiples,  more  than  one  value  will  be 
found.  For  convenience  the  smallest  might  be  designated, 
although  this  is  not  important.  If  it  forms  no  compound 
with  hydrogen,  it  is  necessary  to  determine  its  ratio  of  com- 
bination with  some  element,  the  equivalent  weight  of  which 
has  been  determined.  Many  of  the  elements  do  not  com- 
bine with  hydrogen,  or,  if  they  do  so  combine,  they  form 
compounds  not  so  well  suited  for  analysis  as  those  with 
some  other  element.  On  the  other  hand,  most  of  the 
elements  do  combine  with  oxygen  and  furnish  compounds  143 
available  for  analysis.  With  chlorine,  also,  many  advan- 
tageous compounds  are  formed.  And  so,  historically,  the 
oxides  and  chlorides  have  been  more  frequently  used  than 
the  hydrides,  and  in  some  instances  other  and  more  com- 
plicated compounds  than  these  have  served. 

To  determine  the   equivalent  weight,  therefore,  it  is  ne-  144 
cessary  to  ascertain  by  experiment  ivhat  mass  of  the  element 
combines  ivith  1  gram  of  hydrogen,  or,  if  this  is  impracti- 
cable, with  7.94  grams  of  oxygen,  or  85.189  grams  of  chlorine, 
or  with  the  equivalent  mass  of  some  other  substance. 

71 


72          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

145  There  is  no  need  to  consider  here  the  details  of  experi- 
mental procedure.     The   most  refined  analytical  methods 
known  and  available  to  chemists  have  been  brought  to  bear 
upon  the  determination  of  these  fundamental  values.     Not 
by  any  means  the  same   degree  of  accuracy  has  been  at- 
tained in  all  instances.     The  values  given  for  the  combining 
weights  in  Table  XI,  No.  644,  have  in  most  instances  an 
uncertainty  of  one  or  two  units  in  the  last  figure.     The 
greatest  accuracy  is  claimed  for  that  of  silver,  with  an  un- 
certainty of  less  than  four  units  in  more  than  one  hundred 
thousand,  an  accuracy  "  which  has  scarcely  been  obtained 
elsewhere  in  the   exact   sciences,   much  less  surpassed."  * 
The  name  of  Stas  (1860-1865),  a  Belgian  chemist,  is  mem- 
orably associated  with  this  great  work. 

146  Several  other  values  show  an  uncertainty  of  only  a  few 
units  in  ten  thousand  or  more,  while  in  others  it  is  as  much 
as  one  per   cent.     The   combining   ratios  of   oxygen  and 
chlorine  with  hydrogen  are  especially  important,  being  the 
values  upon  which  many  of  the  others  depend,  and  vast 
labor  and  great  skill  have  been  brought  to  bear  upon  their 
determination.     In  spite  of  this,  the  equivalent  of  oxygen, 
until  a  comparatively  recent  date,  has  been  affected  by  an 
uncertainty  as  great  as  one  part  in  two  hundred.     For  this 
reason  it  has  been  proposed  to  fix  this  value  as  eight— 
that  is.  to  make  8  grams  of  oxygen  the  base  of  the  sys- 
tem instead  of  1  gram  of  hydrogen,  letting  the  uncertainty 
lie  upon  the  value  for  hydrogen,  the  equivalent  weight  of 
which  would  become  one  and  a  small  fraction.     The  com- 
bining weights  reckoned  on  this  basis  (0  =  16)  are  also 
given  in  Table  XI,  No.  644. 

147  By  experiments  involving  the  greatest  skill  and  most 
elaborate  apparatus,  Morley,  of  Cleveland  (1895),  and  others, 
have  determined  the  mass  of  oxygen  which  combines  with 
2  grams  of  hydrogen  as  15.879,  with  a  probable  error  of 

*  Ostwald  (Walker).  "  Outlines  of  General  Chemistry." 


DETERMINING  EQUIVALENT  WEIGHTS  73 

only  a  few  units  in  about  sixteen  thousand.     A  few  of 
Morley's  results  are  here  quoted  as  of  interest : 

15.877 
15.877 
15.877 
15.878 
15.879 
15.881 
15.881 
15.882 


15.8792  =  the  mean  of  these  and  others. 

As  of  special  interest,  also,  in  connection  with  your  ex-  148 
periment  under  Law  4,  Chapter  II  (No.  41/2),  are  quoted 
some  recent  results  in  determining  with  the  utmost  exact- 
ness the  mass  of  zinc  which  combines  with  16  grams  of 
oxygen,  by  converting  a  weighed  quantity  into  nitrate, 
igniting,  and  weighing  the  oxide  obtained  : 

65.459 
65.445 
65.459 
65.440 
65.489 
65.475 
65.437 
65.447 


65.457  * 

In  the  case  of  some  of  the  metals,  the  experimental  de-  149 
termination  of  the  ratio  of  hydrogen  displacement,  as  illus- 
trated in  your  experiments  (Nos.  41/3  and  41/4),  is  useful, 
but  rather  as  a  secondary  method  of  control  than  as  a  direct 
determination  of  the  equivalent  weight. 

*  Morse  and  Arbuckle,  American  Chemical  Journal,  xx,  195  (1898). 


74          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


2.  Determination  of  the  Combining  Weight  of  an 
Element 

150  The  choice  of  that  multiple  of  the  equivalent  weight 
which  shall  be  designated  as  the  combining  weight  is  con- 
trolled by  such  one  or  several  of  the  relations  given   in 
Chapter  V  as  may  be  applicable  to  the  element  in  question. 
In  the  event  of  conflicting  indications,  the  law  of  Gay-Lus- 
sac  probably  carries  the  greatest  weight,  and  next  to  this 
the  law  of  Dulong  and  Petit.      The  laws  of  Eaoult  have 
come  into  use  in  only  comparatively  recent  years,  and  have 
given  valuable  indications  in  many  cases  in  which  the  data 
for  the  application  of  the  other  laws  were  lacking. 

151  Besides  the  reasons  for  the  choice  of  multiples,  which 
are    found    in  the    correlation  of   the   specific   properties 
studied  in  Chapter  V,  a  very  important  aid  is  obtained  in 
considering  the  relation  of  the  element  to  other  elements 
through  its  general  properties.     This  relation  is  embodied 
in  the  law  of  periodicity  (see  Chapter  VIII,  Nos.  436  and  589, 
Part  I),  the  presentation  of  which  is  best  deferred  until 
after  a  somewhat  detailed  descriptive  study  of  the  elements 
themselves.     Suffice   it   for  the  present   to  state,  by  way 
of  illustration,  that  the  relation  of   carbon  to  the  other 
elements,  now  expressed  by  the  law  of  periodicity  as  de- 
pendent on  the  combining  weight  12,  would  be  quite  inex- 
pressible as  dependent  on  any  other  multiple  of  its  equiva- 
lent weight  3,  if  the  other  elements  retained  their  present 
values. 

152  It  may  be  well  to  emphasize  by  repetition  here  what  is 
implied  in  all  the  foregoing  study,  that  these  relations  with 
specific  properties  are  used  only  to  determine  the  choice  of 
that  exact  multiple  by  a  whole  number  of  the  equivalent 
weight  which  shall  be  used  as  combining  weight,  and  not 
to  determine  the  fundamental  ratio  itself,  which  is  expressed 
in  the  equivalent  weight.      This  value   is  determined  by 
chemical  analysis  with  a  precision  which,  save  in  a  few  in- 


JOSEPH  LOUIS  GAY-LUSSAC 

B.  France,  1778.     D.  Paris,  1850. 

(See  Nos.  47/T,  89,  220.) 


DETERMINING  EQUIVALENT  WEIGHTS  f5 

stances,  far  exceeds  that  reached  in  the  measurement  of  the 
specific  properties.  The  approximations  in  the  latter  are, 
however,  usually  sufficient  to  distinguish  clearly  between 
different  multiples. 

« 
3.  Determination  of  the  Formula  of  a  Compound 

The  first  step  in  the  solution  of  this  problem  must  be  to  153 
determine  qualitatively  what  elementary  constituents  the 
given  compound  contains.  It  suffices,  and  may  be  more 
convenient,  to  learn  the  proximate  constituents,  if  the  com- 
position of  the  latter  is  known.  Thus  carbon  dioxide  may 
be  recognized  as  a  constituent  of  sodium  carbonate  (com- 
pare Exps.  Nos.  35  and  81/i),  and  by  this  it  is  known  that 
carbon  and  oxygen  are  among  its  elementary  constituents. 
It  is  often  more  practicable  to  convert  an  elementary  con- 
stituent into  some  recognizable  compound,  than  to  separate 
and  identify  it  in  its  elementary  condition.  Thus,  if  a 
compound  is  combustible,  and  water  is  identified  as  a  prod- 
uct of  its  combustion,  the  presence  of  hydrogen  as  a  con- 
stituent is  proved  (compare  Exps.  34/2  and  34/4). 

The  second  step  must  be  to  ascertain,  as  accurately  as  154 
possible,  the  quantities  of  the  elements  present  in  a  meas- 
ured quantity  of  the  compound.  And  here  likewise,  it 
may  be  necessary  to  convert  the  elements  quantitatively  into 
forms  of  known  composition,  suitable  for  measurement. 
The  results  of  such  quantitative  determination  are  usually 
expressed  as  parts  found  in  one  hundred  parts  of  the  com- 
pound taken. 

To  deduce  a  formula  when  the  percentage  composition  155 
is  known,  divide  the  percentage  of  each  constituent  by  the 
combining  weight  of  the  same.  A  series  of  quotients  is  thus 
obtained  which  should  stand  to  each  other  in  a  ratio  closely 
approximating  that  of  whole  numbers ;  if  the  whole  num- 
bers desired  do  not  appear  on  inspection,  divide  the  quo- 
tients by  the  smallest  of  the  series.  Write  the  symbols  of 


76          ELEMENTARY   PRINCIPLES  OF  CHEMISTRY 

the  elementary  constituents  together  to  form  the  symbol  of 
the  compound,  and  attach  to  them,  as  coefficients  (written 
below  the  line),  the  simplest  set  of  whole  numbers  which 
stand  in  the  ratio  of  the  quotients.  This  formula  shows 
the  percentage  composition  of  the  substance,  and  the  sum 
of  the  constituent  weights  becomes  its  combining  weight, 
unless  there  be  found  some  reason  for  choosing  a  multiple 
of  this  formula  and  this  combining  weight,  as  indicated  by 
the  law  of  Gay-Lussac,  or  those  of  Eaoult.  Of  these  the 
former  is  reckoned  as  giving  the  surer  indication.  There 
are  many  compounds,  however,  to  which  neither  can  be 
applied. 

155/1          The  following  example  of  actual  experimental  results  is  taken  from 
a  recent  journal :  * 

Experiment  I.  Experiment  II. 

Carbon 12.00  per  cent  11.69  per  cent 

Hydrogen 3.98        "  4.02 

Nitrogen 6.77 

Bromine. .  .  77.56        " 


100.31 


12.00  -5-  11.9  =  1.008 
3.98 -f-    1.0  =  3.98 
6.77  -f-  13.9  =  0.487 

77.56  -s-  79.3  =  0.978 


1.008  -^  0.487  =  2.07 
3.98    -=-0.487  =  8.17 
0.487  -=-  0.487  =  1.0 
1.978  -r-  0.487  =  2.01 


Hence  is  deduced  the  formula  C2H8NYBr2,  which  expresses  the  follow- 
ing percentages  to  which  the  experimental  values  approximate : 

Carbon  =11.65 
Hydrogen  =  3.92 
Nitrogen  =  6.80 
Bromine  =  77.63 


100.00 

156  EXAMPLES.— (1)  Deduce  the  formula  of  the  compound  from  the 
following  data :  92.30  per  cent  of  carbon,  7.70  per  cent  of  hydrogen ; 
specific  gravity  as  a  gas  (H  =  1)  is  approximately  38. 

*  American  Chemical  Journal,  vol.  xx,  p.  56  (January,  1898). 


DETERMINING  EQUIVALENT  WEIGHTS  Y? 

(2)  Also  for  40.00  per  cent  of  carbon,  6.67  per  cent  of  hydrogen, 
and  53.33  per  cent  of  oxygen ;  specific  gravity,  as  a  gas,  is  approxi- 
mately 29. 

(3)  Also  for  78.86  per  cent  carbon,  10.60  per  cent  hydrogen,  10.53 
per  cent  oxygen. 

(4)  Assume  that  1  gram  of  a  substance  (e.  g.,  alcohol)  containing 
only  carbon,  hydrogen,  and  oxygen  yields  by  burning  1.913  grams  of 
carbon  dioxide  and  1.173  grams  of  water  (the  quantity  of  oxygen  is 
assumed  to  be  the  difference  between  the  total  and  the  sum  of  the  car- 
bon and  the  hydrogen) ;  assume  that  the  specific  gravity  of  the  gas 
is  approximately  23 ;  deduce  the  percentage  of  carbon,  hydrogen,  and 
oxygen,  and  the  formula  of  the  substance. 

(5)  Experiment  gives  for  ferric  chloride  the  vapor-density  10.7  (air  =  1) 
and  the  percentage  of  chlorine  65.76 ;  also  the  specific  heat  of  iron  as 
0.114;  assume  for  the  combining  weight  of  chlorine  35.2  and  deduce 
the  combining  weight  of  iron  and  the  formula  of  iron  chloride  (Meyer 
and  Griinwald). 

(6)  What  percentage  of  chlorine  is  contained  in  ammonium  chloride? 

(7)  What  is  the  percentage  of  iodine  in  mercurous  iodide?    In  mer- 
curic iodide  t 

(8)  Assume  that  10  grams  of  pure  iron  displace  0.36  of  a  gram  of 
hydrogen  from  hydrochloric  acid ;  calculate  the  equivalent  weight  of 
iron. 

(9)  What  weight  of  oxygen  should  be  obtained  by  heating  10  grams  of 
pure  potassium  chlorate  ? 

(10)  What  is  the  percentage  of  carbon  dioxide  contained  in  calcium 
carbonate  ?  * 


CHAPTER  VII*      . 

THE    ATOMIC    THEORY 

157  IT  is  the  purpose  of  this  chapter  to  present  under  this 
general  title  the  prevailing  theories  which  have  been  de- 
vised  to  explain   the  facts   already  set   forth,  as  well   as 
many  other  facts  impracticable  of  treatment  in  an  elemen- 
tary study. 

158  Some  writers  on  the  history  of  chemistry  endeavor  to 
trace  the  origin  of  the  atomic  theory  back  to  Greek  and 
Latin  speculative  writers,  who  did  indeed  discuss  the  nature 
of  matter,  its  infinite  divisibility,  and  kindred  subjects;  but 
this  was  rather  metaphysical  speculation,  and  may  hardly 
be  regarded  as  related   to   physical  science  in  the  strict 
meaning  of  the  term. 

159  To  Dalton,  a  chemist  and  physicist  of  Manchester,  Eng- 
land, is  credited  the  invention  of  the  atomic  theory,  since 
he  was  the  first  to  give  it  quantitative  form,  and  to  make  it 
a  truly  scientific  hypothesis,  to  be  tested  by  experiment  and 
observation.     This  he  did  between  1803  and  1806,  and  he 
was  led  to  the  conception  largely  by  his  discovery  of  the 
fact  of  multiple  proportions.     Since  then  the  theory  has 
been  greatly  modified  by  change  and  extension,  but  still 
preserves  his  fundamental  idea. 

160  In  order  to  present  the  theory  as  a  whole,  and  logically 

*  If  the  instructor  desires  to  defer  the  presentation  of  the  Atomic 
Theory  until  later  in  the  course,  there  is  nothing  in  the  arrangement 
of  the  subject-matter  to  hinder  so  doing. 

78 


THE  ATOMIC  THEORY  79 

rather  than  chronologically,  it  is  necessary  to  give  atten- 
tion, first,  to  a  purely  physical  hypothesis  as  to  the  consti- 
tution of  matter.  The  assumption  which  most  satisfac- 
torily explains  many  facts  in  the  domain  of  physics  is  that 
gross  matter — that  is,  matter  as  it  appears  to  the  senses — is 
an  aggregation  of  very  small  material  particles,  separated 
by  intervening  spaces,  and  that  these  particles  are  the 
units  (or  individuals,  so  to  speak)  upon  which  act  different 
kinds  of  energy,  such  as  heat,  light,  and  electricity.  The 
supposition  is  that  substances  (for  example,  glass),  although 
they  appear  homogeneous,  are  in  reality  grained,  and  would 
so  appear  to  a  sufficiently  magnified  sense — as  a  pile  of 
shot,  -at  a  distance,  would  seem  homogeneous,  but,  seen 
closely,  would  show  its  grained  structure. 

These  particles  are  called  molecules,  and  the  theory  is  101 
named  the  molecular  theory.  Upon  it  depends  largely  the 
explanation  of  the  important  phenomena  of  light  and  of 
heat,  such  as  expansion  and  contraction  with  change  of 
temperature,  the  solid,  liquid,  and  gaseous  states,  and, 
in  respect  to  the  latter,  the  law  of  Boyle  and  that  of 
Charles. 

These  molecules  are  reckoned  as  real  magnitudes,  fur-  162 
nishing  as  definite  a  basis  for  mathematical  reasoning  as  if 
they  could  be  individually  weighed  on  the  balance.  They 
are  much  smaller  than  anything  revealed  by  the  most  pow- 
erful microscope,  yet  they  are  capable  of  approximate  meas- 
urement by  indirect  calculation.  Lord  Kelvin,  the  eminent 
English  physicist,  has  estimated  that  if  a  drop  of  water 
were  magnified  to  the  size  of  the  earth,  and  its  molecules  in 
the  same  proportion,  the  mass  would  appear  more  coarsely 
grained  than  a  heap  of  small  shot,  but  less  coarsely  grained 
than  a  heap  of  baseballs.  Or  again,  a  cube  one  four-thou- 
sandth of  a  millimeter  or  one  one-hundred-thousandth  of  an 
inch  on  the  edge  is  about  the  smallest  mass  to  be  seen  by  a 
good  microscope,  and  this  contains  from  sixty  millions  to 
one  hundred  millions  of  molecules.  Such  magnitudes  are 


80          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

so  far  beyond  the  range  of  ordinary  experience  that  they 
seem  as  inconceivably  small  as  the  celestial  dimensions  seem 
inconceivably  large. 

The  atomic  theory  (or  the  atomic-molecular  theory,  as 
it  might  be  called)  in  its  present  form  involves  the  follow- 
ing fundamental  assumptions : 

163  1.  The  molecular  constitution  of  matter. — It  is  assumed 
that  gross  matter  is  an  aggregation  of  very  minute  mate- 
rial particles,  separated  by  intervening  spaces.     These  par- 
ticles, called  molecules,  act  as  units  to  all  forces  other  than 
chemical. 

164  2.  The  kinetic  theory  of  gases  (due  largely  to  Clausius, 
1857)  assumes  that  in  the  gaseous  condition  the  separating 
spaces  are  considerable  as  compared  with  the  size  of  the 
molecules ;  that  the  molecules  are  in  rapid  motion  in  all 
directions,  colliding  constantly  with  each  other  and  with 
the  walls  of  the   containing  vessel,  and,  being  perfectly 
elastic,  rebounding    after    every   collision ;   and  that  gas 
pressure  is  due  to  this  impact  on  the  walls.     From  these 
assumptions,  and  by  the  application  of  the  laws  of  me- 
chanics, may  be  deduced  the  laws  of  Boyle  and  Charles, 
which  also  have  a  purely  experimental  basis,  as  has  been 
already  described. 

165  3.  Avogadro's  hypothesis.— It  is  assumed  that  equal  vol- 
umes of  all  gases,  independently  of  their  chemical  char- 
acter, at  the  same  temperature  and  pressure,  contain  the 
same  number  of  molecules.     This  was  put  forth  as  a  hy- 
pothesis by  Avogadro  in  1811,  but  it  may  also  be  deduced 
from  the  kinetic  theory  of  gases  which  was  developed  con- 
siderably later. 

166  4.  The  chemical  definition  of  a  molecule  defines  it  as  the 
smallest  mass  of  a  substance  in  which  the  properties  of  the 
substance  inhere;  that  is,  the  identity  of  a  substance  is 
conceived  as  resident  in  its  molecule.     It  is  assumed  that 
all  molecules  of  the  same  substance  are  alike  and  have  the 
same  mass. 


THE  ATOMIC  THEORY  81 

5.  As  to  molecular  weights. — It  is  assumed  that  the  rela-  167 
tive  mass  of  molecules  of  different  substances,  referred  to 

the  molecule  of  hydrogen  as  unity,  is  equal  to  the  specific 
gravity  of  the  substance  in  gaseous  condition,  referred  to 
hydrogen  as  standard.  It  follows  that  the  values  which 
have  been  called  the  combining  weights  of  compounds  are 
by  this  theory  called  their  molecular  weights  (in  this  sense 
not  expressible  in  grams),  and  that  the  molecular  weight  of 
hydrogen,  and  of  some  other  elementary  gases,  is  twice  the 
combining, weight.  This  assumption  is  a  direct  deduction 
from  the  laws  of  Gay-Lussac  (see  Part  I,  Nos.  47,  90/l5  and 
90/2)  and  the  hypothesis  of  Avogadro. 

6.  The  divisibility  of  the  molecule  of  a  compound  into  168 
smaller  parts  which  are  unlike  each  other,  and  unlike  the 
original  molecule,  is  assumed  because  a  measured  mass  of 
the  compound  can  be  separated  into  smaller  masses  of  its 
elementary  constituents.     Thus,  since  18  grams  of  water 
can  be  separated  into  2  grams  of  hydrogen  and  16  grams 

of  oxygen,  it  is  assumed  that  the  molecule  of  water,  weigh- 
ing nine  times  as  much  as  the  molecule,  of  hydrogen,  can 
be,  and  in  the  decomposition  of  water  is,  separated  into 
smaller  parts  of  two  different  kinds,  called  atoms,  one  in 
the  aggregate  showing  the  properties  of  hydrogen,  and  the 
other  those  of  oxygen.  Compare  No.  172. 

7.  The  divisibility  of  the  molecule  of  an  element,  at  least  169 
of  some  elements,  is  assumed,  and  the  assumption  is  based 

on  reasoning,  of  which  the  following  is  an  example  :  It  is  a 
fact  that  one  gas-volume  of  hydrogen  and  one  gas-volume 
of  chlorine  combine  and  form  two  gas-volumes  of  hydro- 
chloric acid  (see  Part  I,  No.  49/j).  It  is  assumed  that  two 
gas-volumes  of  the  compound  contain  twice  as  many  mole- 
cules as  one  gas-volume  of  hydrogen  and  twice  as  many  as 
one  gas-volume  of  chlorine.  It  is  also  assumed  that  every 
molecule  of  hydrochloric  acid  contains  its  smaller  particle 
of  hydrogen  and  of  chlorine.  Therefore  it  is  assumed  that 
every  molecule  of  hydrogen,  likewise  of  chlorine,  is  divisible 


82          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

into  at  least  two  equal  and  like  parts,  since  the  hydrogen 
molecules  are  distributed  among  twice  their  number  of 
molecules  of  hydrochloric  acid.  Exactly  similar  reasoning 
leads  to  the  assumption  that  the  molecules  of  oxygen  in 
forming  water,  and  those  of  nitrogen  in  forming  ammonia, 
are  divided  into  at  least  two  equal  and  like  parts.  And 
the  same  is  true  of  most  of  the  elementary  gases.  These 
smaller  particles  are  named  atoms. 

170  This  assumption  in  distinguishing  between  the  mole- 
cule and  the  atom  of  elements  interprets  the  facts  concern- 
ing vapor-density  (see  Nos.  72,  etc.,  93,  and  94)  as  indicating 
that  the  molecule  of  hydrogen  and  that  of  most  of  the 
elementary  gases  contain  two  atoms ;  that  the  molecule  of 
iodine  contains  two  atoms  at  low  temperature,  but  only  one 
at  high — in  other  words,  the  atom  and  molecule  become  the 
same ;  likewise  the  molecule  of  sulphur  contains  seven  or 
eight  atoms  at  low  and  two  at  high  temperature ;  that  of 
phosphorus  and  that  of  arsenic  contain  four  atoms ;  while 
the  molecules  of   sodium,  potassium,  zinc,  cadmium,  and 
mercury  contain  Jmt  one  atom.     See  Nos.  139  and  141. 

171  8.  The  atom  is  defined  as  the  smallest  mass  of  each  ele- 
mentary substance  that  is  found  in  any  molecule;  it  is  the 
unit  upon  which  chemical  force  acts,  remaining  undivided 
through  all  changes.     It  is  assumed  that  all  atoms  of  the 
same  element  are  alike,  but  unlike  the  atoms  of  every  other 
element. 

172  It  is  customary  to  speak  of  the  atoms  of  hydrogen  and 
of  the  atoms  of  oxygen,  yet  we  may  not  be  justified  in 
assuming  that  an  aggregation  of  such  atoms,  uncombined 
in  molecules,  would  show  the  properties  of  hydrogen  and 
of  oxygen. 

178  9.  As  to  atomic  weights. — It  is  assumed  that  all  chem- 
ical changes  are  due  to  the  interaction  of  atoms;  and  that 
the  relative  mass  of  atoms  of  different  elements,  referred  to 
the  atom  of  hydrogen  as  unity,  is  constant  and  numerically 
equal  to  the  combining  weight  of  the  element.  Therefore 


THE  ATOMIC  THEORY  83 

the  values  which  have  been  called  combining  weights  of  the 
elements  are  by  this  theory  called  the  atomic  weights  (in 
this  sense  not  expressible  in  grams).  It  follows  that  the 
formula  of  a  compound  shows  the  kind  and  number  of 
atoms  in  its  molecule. 

This  assumption  constituted  the  atomic  theory  as  first  174 
announced  by  Dalton  in  1804.     It  is  simply  a  theoretic 
interpretation,  or  explanation,  of  the  facts  embodied  in  the 
laws  of  fixed,  multiple,  and  equivalent  proportions. 

10.  As  to  heat  capacity. — It  is  assumed  that  all  atoms  175 
have  the  same  heat  capacity  (see  Nos.  101  and  102).     This 

is  but  the  theoretic  interpretation  of  the  law  of  Dulong 
and  Petit. 

11.  As  to  Raoult's  laws. — The  theoretic  statement  is  that  176 
the  effect  of  a  solute  in  lowering  the  freezing  point  and  in 
raising  the  boiling  temperature  of  a  solvent  is  dependent 

on  the  number  and  not  on  the  kind  of  molecules  of  the 
solute  present  in  a  specified  mass  of  the  solvent.  The 
observations  concerning  sulphur  and  phosphorus  and  iodine 
in  solution  are  interpreted  as  indicating  eight,  four,  and 
two  atoms  respectively  in  the  molecule  (compare  Nos.  116, 
122,  135,  139,  and  141).  The  exceptional  values  for  com- 
pounds, such  as  those  seen  in  the  last  three  items  of  the 
table,  No.  120,  are  thought  by  some  to  indicate,  for  the 
substances  when  dissolved  in  the  specified  solvent,  a  molec- 
ular weight  which  is  double  the  formula  weight  given  in 
the  table.  On  the  other  hand,  values  such  as  those  seen  in 
the  last  five  items  of  No.  121  and  in  the  last  item  of  No.  133 
are  interpreted  as  indicating,  not  that  the  molecular  weights 
of  the  substances  in  question  are  one  half  those  assigned  in 
the  table,  but  that  the  substances  are  actually  decomposed 
in  the  conditions  of  observation  into  elementary  or  into 
proximate  constituents,  so  that  there  are  twice  as  many 
molecules  present  as  there  would  be  without  decomposi- 
tion. This  assumption  as  to  the  peculiar  condition  of  some 

substances  when  dissolved  in  some  solvents  is  the  basis  of 

7 


84          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

what  is  known  as  the  theory  of  electrolytic  dissociation  or  of 
ionization.  It  was  advanced  by  Arrhenius  in  1887,  and  it 
includes  the  theoretic  interpretation  of  many  of  the  phe- 
nomena of  solution  besides  those  pertaining  to  the  freezing 
point  and  to  the  boiling  temperature. 

177  12.  As  to  the  structure  of  molecules.— It  is  assumed  that 
the  properties  of  substances  are  affected  not  only  by  the 
kind  and  number  of  atoms  in  the  molecule,  but  also  by 
their  arrangement,  grouping,  or  linkage. 

178  The  discovery  in   1828  by  Wohler  that  two  different 
substances  may  have    the   same   percentage   composition 
found  no  explanation  in  the  theory  of  that   time,  which 
assumed  that  the  properties  of  the   compound  were  de- 
pendent only  on  the  kind  and  number  of  its  constituent 
atoms.    Since  then  very  many  instances  have  been  revealed 
of  substances  which  are  identical  in  percentage  composi- 
tion, but  still  very  different  in  properties  (compare  ^os. 
37/7,  85,  85/j,  and  86).     This  has  led  to  the  assumption 
of  molecular  structure  to  explain  the  existence  of  such 
substances,  and   many  of  the   most   conspicuous  achieve- 
ments of  modern  chemistry  may  be  properly  regarded  as 
the  outcome  of  this  conception,  or  of  experiments  guided 
by  it. 

179  Substances  having  the  same  percentage  composition, 
but  not  identical,  are  called  isomers.     Of  these  there  are 
two  varieties — the  polymers  and  the  metamers.     The  poly- 
mers are  substances  which  have  the  same  percentage  com- 
position, but   differ   in  molecular  weight.     For   example : 
the  two  substances  acetylene,  C2H2,  and  benzene,  C6H6,  are 
polymers.     In  terms   of   the   theory,  the  molecule  of  the 
first  contains  two  atoms  of  carbon  and  two  of  hydrogen, 
while  that  of  the  second  contains  six  atoms  of  carbon  and 
six  of  hydrogen. 

180  The  metamers  are   substances  which   have    the   same 
percentage  composition  and  the  same  molecular  weight. 
Their  difference  of  properties  is  theoretically  explained  as 


THE  ATOMIC  THEORY  85 

due  to  difference  in  the  grouping  of  the  constituent  atoms 
of  the  molecule.  This  is  expressed  in  their  formulas  by  a 
difference  in  the  grouping  of  the  symbols.  For  example  : 
the  first  instance  of  isomerism,  discovered  by  Wohler,  was 
in  the  two  substances  ammonium  cyanate,  a  salt,  NH4CNO, 
and  urea  (NH2)2CO,  a  very  different  substance  having  not 
even  the  general  characteristics  of  the  salts.  The  differ- 
ence in  structure  is  shown  in  the  different  arrangement  or 
grouping  of  the  elementary  symbols. 

Evidence  as  to  structure. — The  subject  of  structure  finds  181 
its  greatest  development  in  the  study  of  the  carbon  com- 
pounds, usually  called  organic  chemistry,  and  no  detailed 
consideration  of  it  is  judged  suitable  for  a  course  having 
the  scope  of  this  one.  It  is  desired,  however,  to  give  a 
suggestion  concerning  the  kind  of  evidence  upon  which 
assumptions  as  to  structure  are  based.  For  illustration, 
take  the  substance  known  as  acetic  acid.  It  contains  the 
elements  carbon,  hydrogen,  and  oxygen.  The  percentage 
of  these  gives  the  formula  CH20,  the  combining  weight  of 
which  would  be  30.  But  the  specific  gravity  of  the  sub- 
stance in  gaseous  condition  indicates  the  combining  weight 
60;  therefore  the  molecular  formula  of  the  substance  is 
C2H402.  This  is  polymeric  with  another  very  different 
substance  which  has  the  formula  CH20.  Now,  it  is  ob- 
served that  the  substance  C2H402  acts  as  an  acid — that  is, 
it  contains  hydrogen  which  can  be  replaced  by  the  action 
of  metals,  forming  a  series  of  well  defined  salts.  But  ex- 
periment shows  also  that  only  one  fourth  of  the  hydrogen 
contained  can  be  thus  replaced.  The  theoretic  interpreta- 
tion of  this  is,  that  one  of  the  four  hydrogen  atoms  is  held 
or  linked  in  the  molecule  in  a  manner  somehow  differing 
from  that  of  the  other  three,  and  this,  the  first  step  in 
differentiating  the  atoms  in  the  structure  of  the  molecule, 
is  expressed  by  writing  the  formula  H(C2H302). 

Again,  experiment  shows  that  by  acting  upon  acetic    181/1 
acid  with  a  certain  substance  there  is  obtained  from  it  a 


86          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

substance  which,  when  compared  with  the  original  in  com- 
position, shows  the  loss  of  one  atom  of  hydrogen  and  one 
of  oxygen  and  the  gain  of  one  atom  of  chlorine — that  is, 
one  atom  of  chlorine  has  been  substituted  for  one  of  hydro- 
gen and  one  of  oxygen,  but  no  more  than  these  two  can 
be  thus  substituted.  The  theoretic  interpretation  of  this 
is  that  one  atom  of  hydrogen  and  one  of  oxygen  are  held 
in  a  peculiar  manner  not  shared  by  the  other  atoms  of 
hydrogen  and  oxygen.  Furthermore,  the  derived  sub- 
stance, C2H3OC1,  does  not  show  the  property  of  substi- 
tuting a  metal  for  the  hydrogen ;  therefore  it  is  assumed 
that  the  hydrogen  atom,  thus  associated  with  the  oxygen 
atom  in  leaving  the  molecule,  is  the  same  that  in  the  origi- 
nal substance  was  replaceable  by  a  metal.  This,  the  second 
step  in  solving  the  molecular  structure,  is  expressed  by 
writing  the  formula  HO(C2H30). 

181/2  It  is  next  shown  by  experiment  that  acetic  acid  can  be 
made  synthetically,  by  a  series  of  changes  not  necessary  to 
detail,  from  a  substance  whose  molecule  contains  but  one 
carbon  atom,  three  hydrogen  atoms,  and  the  group  OH. 
Its  structure  is  shown  by  the  formula  CH3OH.  The  change 
of  this  into  acetic  acid  involves  the  addition  to  the  mole- 
cule, CH3OH,  of  a  carbon  atom  from  a  source  outside  of 
itself,  and  some  subsequent  intermediate  modifications ;  but 
it  is  assumed  that  the  atomic  group  CH3  passes,  itself 
unmodified,  from  the  parent  molecule,  CH3OH,  into  the 
product,  HO(C2H30),  and  continues  to  exist  in  the  latter. 
This  resolves  the  atomic  group  C2H30  into  the  groups  CO 

181/3  and  CH3.  Thus  the  original  molecule  containing  two  car- 
bon, four  hydrogen,  and  two  oxygen  atoms  (C2H402)  has 
been  resolved  into  atomic  groups  as  expressed  by  the  sym- 
bols HO,  and  CO,  and  CH3.  This  is  shown  in  the  struc- 
tural or  constitutional  formula  CH3-CO*OH. 
182  By  observations  and  assumptions,  such  as  these  just 
described,  the  structures  of  hundreds  of  substances  have 
been  determined,  many  of  them  very  complicated.  Not 


THE  ATOMIC  THEORY  87 

only  is  this  true,  but  also  that  many  natural  substances, 
and  even  many  never  found  in  nature,  have  been  made 
artificially  by  building  them  up  from  simpler  substances  as 
indicated  by  the  atomic  groups  in  their  assumed  structure. 
It  is  doubtful  if  any  branch  of  natural  science  can  show 
more  numerous  instances  of  brilliant  achievements  in  fact, 
realized  under  the  guidance  of  theoretic  conceptions,  than 
can  synthetic  chemistry. 

13.  As  to  space  relations  of  atoms,  or  stereo-isomerism. — It  is  183 
assumed  that  the  properties  of  substances  may  be  influenced  to 
a  limited  extent  by  the  space  relations  of  the  atomic  groups. 

The  discovery  made  by  Pasteur  in  1848,  that  substances  184 
might  have  not  only  the  same  percentage  composition,  the 
same  molecular  weight — i.  e.,  the  same  kind  and  number  of 
atoms  in  the  molecule — but  even  the  same  atomic  grouping, 
and  still  differ  slightly  in  respect  to  certain  properties, 
could  not  be  explained  by  the  then  existing  theories.  The 
substance  in  which  this  phenomenon  was  first  observed  by 
Pasteur  is  tar  tar  ic  acid,  found  in  the  grape  and  other  fruits. 
The  properties  in  which  the  slight  difference  is  manifested 
are  crystalline  form,  and  behavior  toward  polarized  light. 
It  would  be  entirely  impracticable  fully  to  describe  here 
either  the  phenomenon  or  the  theory.  Let  it  suffice  to 
say  that  Pasteur  observed  at  least  two  varieties  of  tartaric 
acid.  One  when  in  solution  rotates  to  the  right  the  plane 
vin  which  a  ray  of  light  is  polarized  ;  the  other  rotates  it  to 
the  left.  The  two  varieties,  when  crystallized,  show  two 
kinds  of  crystals,  one  of  which,  as  to  arrangement  of  angles 
and  faces,  is  like  the  image  of  the  other  as  seen  in  a  mirror. 
Yet,  as  to  behavior  in  all  their  reactions,  the  two  varieties 
are  alike,  and  therefore,  it  must  be  assumed,  have  the  same 
structure  or  atomic  grouping.  This  phenomenon  is  called 
physical  isomerism,  or  stereo-isomerism.  Many  other  ex- 
amples of  it  have  since  been  discovered. 

In  1874  Le  Bel  and  van't  Hoff,  independently  of  each   185 
other,  announced  a  theory   designed   to   account  for   the 


88          ELEMENTARY  PRINCIPLES  OP  CHEMISTRY 

phenomenon  of  physical  isomerism.  They  both  had  the 
same  fundamental  idea.  According  to  this,  the  carbon  atom, 
which  is  capable  of  uniting  with  four  hydrogen  atoms,  or 
four  groups  of  atoms,  as  seen  in  methane,  CH4,  furnishes 
one  condition  for  the  phenomenon.  It  is  assumed  that 
these  four  atoms  or  groups  are  placed,  with  reference 
to  the  carbon  atom,  like  the  four  apexes  of  a  tetrahedron 
with  reference  to  its  center.  Kow,  it  is  evident  that, 
if  every  one  of  four  such  atoms,  or  groups,  is  different 
from  every  other  one,  there  might  be  in  two  molecules, 
otherwise  alike,  the  same  difference  in  the  position  of  the 
four  with  reference  to  the  carbon  atom  as  there  is  in  the 
four  apexes  of  a  tetrahedron  with  reference  to  its  center, 
compared  with  the  same  as  seen  in  the  image  of  the  tetra- 
hedron reflected  in  a  mirror.  A  carbon  atom  thus  linked 
with  four  different  atoms,  or  groups,  is  called  asymmetric, 
and  its  presence  in  the  molecule  is  supposed  by  the  the- 
ory to  be  the  cause  of  stereo-isomerism.  For  example,  the 
accepted  structure  of  the  molecule  of  lactic  acid,  the  acid 
of  sour  milk,  is  shown  by  the  formula 

H 
CH3—  C— COOH, 

OH 

in  which  it  is  assumed  that  one  carbon  atom  is  linked  with 
four  different  groups,  viz.,  CH3,  and  H,  and  OH,  and  CO'OH. 
It  is,  therefore,  asymmetric,  and  the  substance  should  show 
the  phenomenon  of  physical  isomerism,  as  in  fact  it  does. 
The  theory  has  been  admirably  worked  out,  and  finds  strong 
support  in  many  recognized  facts. 

186  Much  more  is  included  in  this  chapter  than  the  atomic 
theory  of  Dalton  contained,  and  more  than  this  title  accu- 
rately describes.  But  the  title  is  classic,  and  serves  its  pur- 
pose probably  as  well  as  would  any  other  single  phrase. 
That  these  theories  leave  much  unexplained,  is  surely  true. 


HERMANN  VON  HELMHOLTZ 
B.  Germany,  1821.     D.  1894. 
(See  No.  50,  note.) 


THE  ATOMIC  THEORY  89 

That  they  explain  with  entire  satisfaction  all  that  they 
undertake  to  explain,  is  not  wisely  claimed.  That  they 
may  not  in  the  future  be  greatly  modified,  and  even  es- 
sentially changed,  it  is  not  in  accordance  with  the  scientific 
spirit  to  assert.  But  that  they  have  been  and  are  useful  as 
guide  to  investigation  and  as  aid  to  understanding,  is  amply 
proved  by  the  results  achieved. 


CHAPTEE  VIII 

RELATION  BETWEEN  THE  PROPERTIES  OF  THE  ELEMENTS 
IN  GENERAL  AND  THEIR  COMBINING  WEIGHTS 

187  IT  is  the  purpose  in  this  chapter  to  present  a  somewhat 
detailed  description  of  the  first  twenty-five  elements,  taken 
in  the  natural  order — that  is,  the  order  of  their  increasing 
combining  weights,  and  in  connection  with  each  one,  for 
convenience  of  arrangement,  to  give  attention  to  some  of 
its  important  compounds.  This  is  the  subject-matter  often 
designated  as  Descriptive  Chemistry,  and  includes  more, 
perhaps,  than  is  implied,  strictly  speaking,  in  the  title  of 
the  chapter ;  nevertheless,  the  central  idea  of  the  whole  will 
be  found  in  the  relation  to  which  the  title  refers. 


A.    Or  THE  ELEMENTS,  COLLECTIVELY 

188  All  substances,  so  far  as  known,  are  made  up  of  com- 
paratively few  elementary  forms   of   matter,  which  resist 
all  attempts  to  reduce  them  to  simpler  forms.     These,  at 
present,  number    seventy-four,  with    possibly  one  or  two 
additions. 

189  Their  distribution  is  by  no  means  uniform.     Either  free 
or  as  constituents,  all  of  them  are  found  in  the  solid  mass 
of  the  earth ;  some  thirty,  in  the  sea ;  five,  in  the  atmos- 
phere, namely,  hydrogen,  carbon,   nitrogen,   oxygen,  and 
argon  (Roscoe) ;  and,  according  to  the  revelations  of  the 
spectroscope,  at  least  twenty-two  and  possibly  thirty-eight 
have  been  identified  in  the  sun  (Eamsay). 

90 


DESCRIPTION  OF   ELEMENTS  AND  COMPOUNDS      91 


In  quantity,  too,  they  differ  greatly,  so  far  as  known  in 
this  fragment  of  the  universe,  the  earth.  Oxygen  is  the 
most  abundant  of  all.  It  constitutes  nearly  one  quarter 
(23  per  cent)  of  the  atmosphere,  nearly  nine  tenths  (88.9 
per  cent)  of  all  the  water  of  the  globe,  and  nearly  one  half 
(Eoscoe)  of  the  solid  portion  of  the  earth's  crust,  the  other 
half  being  made  up  in  the  main  of  only  seven  other  elements. 
The  following  is  the  estimated  composition  of  the  greater 
portion  of  the  earth's  crust,  not  including  water  (Eoscoe)  : 


190 


Oxygen,        44.0  to  48.7  per  cent 
Silicon,          22.8  to  36.2    "      " 
Aluminium,    9.9  to    6.1    "      " 
Iron,  9.6  to    2.4    "      " 


Calcium,  6.6  to  0.9  per  cent 

Magnesium,  2.7  to  0.1     "      " 

Sodium,  2.4  to  2.5    "      " 

Potassium,  1.7  to  3.1    «      " 


It  is  probable  that  the  interior  mass  of  the  earth  consists 
largely  of  sulphides  (Eamsay). 

Adding  to  the  eight  of  the  foregoing  list  the  following 
six,  namely,  hydrogen,  carbon,  nitrogen,  phosphorus,  sul- 
phur, and  chlorine,  we  have  those  which  constitute  the 
greater  part  of  matter  as  known  to  us.  Twenty-three  more 
might  be  named,  which,  with  those  already  mentioned, 
thirty-seven  altogether,  would  include  about  all  with  which 
we  come  in  contact  in  everyday  life.  Of  the  remainder, 
some  are  found  somewhat  commonly,  although  in  small 
quantities ;  others  are  so  rare  as  to  be  only  scientific  curi- 
osities ;  and  of  still  others  it  may  be  said  that  their  very 
existence  as  elemental  forms  is  open  to  question. 

The  five  most  closely  associated  with  the  living  organism,  191 
whether  plant  or   animal,   are   carbon,  oxygen,   nitrogen, 
hydrogen,    and    sulphur.      Protoplasm,  the    fundamental 
form  of  living  substance,  contains  these,  and  in  proportion 
probably  somewhat  as  follows  : 

%  Carbon,      51     to  55     per  cent 
Oxygen,      20     to  24       "      " 
Nitrogen,   15     to  17       "     " 
Hydrogen,    6.5  to    7.5     "     " 
Sulphur,       0.3  to    2       "      " 


92          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

Besides  these,  phosphorus,  potassium,  calcium,  magne- 
sium, and  iron  are  reckoned  as  essential  to  plant  life. 

All  of  the  foregoing  are  found  in  the  normal  human 
body,  and  in  addition  chlorine,  fluorine,  silicon,  lithium, 
sodium,  and  manganese  (Martin),  If  any  one  more  than 
others  could  be  regarded  as  the  basis  of  living  things,  it  is 
carbon,  by  reason  both  of  its  peculiar  nature  and  its  pre- 
dominating quantity. 

192  Only  comparatively  few  of  the  elements  are  found  free, 
or  uncombined,  and  abundant  in  nature,  at  least  on  the 
earth.     Such  are  oxygen,  nitrogen,  carbon  (as  coal),  and 
sulphur.     Less  abundant,  yet  familiar  either  as  natural  or 
artificial  products,  are  some  of  the  metallic  elements,  namely, 
magnesium,  aluminium,  iron,  nickel,  cobalt,  zinc,  copper, 
tin,  lead,  mercury,  silver,  gold,  and  platinum. 

193  Of  the  whole  list  of  elements  the  following  are  generally 
classed  as  distinctly  non-metallic :   boron,  carbon,  silicon, 
nitrogen,  phosphorus,  oxygen,  sulphur,  selenium,  fluorine, 
chlorine,  bromine,  iodine,  and  the  newly  discovered  sub- 
stances helium  and  argon,  fourteen  in  all.     The  following 
are  classed  sometimes  as  metallic,  sometimes  as  non-metallic  : 
hydrogen,   titanium,    zirconium,   vanadium,   arsenic,  anti- 
mony, and  tellurium.     The  rest  are  metallic. 

194  As  to  physical  properties,  they  vary  through  an  enor- 
mous range.     At  ordinary  temperature,  seven  are  gaseous, 
namely,  hydrogen,  nitrogen,  oxygen,  fluorine,  chlorine,  he- 
lium, and  argon.     Two  are  liquid — bromine,  and  mercury. 

195  The  others  are  solid.    In  boiling  point  they  vary  from  that 
of  hydrogen,  —238°,  to  that  of   carbon,  which  volatilizes 
only  at  the  highest  temperature  of  the  electric  furnace, 
that  is,  3,500°  or  more. 

196  In  density,  the  extremes  are  hydrogen,  one  cubic  centi- 
meter of  which  weighs  0.0000899  of  a  gram,  and  osmium, 
of  which  the  same  volume  weighs  22.48  grams;  that  is, 
osmium  weighs  250,000  times  as  much  as  hydrogen,  volume 
for  volume. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS      93 

In  combining  weight  they  range  from  1  for  hydrogen  to  197 
238  for  uranium. 

In  chemical  activity,  also,  they  vary  greatly.  Thus  fluo-  198 
rine  is  so  reactive,  attacking  so  energetically  everything 
with  which  it  comes  in  contact,  that,  although  its  existence 
was  recognized,  it  could  not  be  isolated  until  Moissan  ac- 
complished the  feat  in  1886.  On  the  other  hand,  argon, 
although  present  in  the  atmosphere  to  the  extent  of  one 
per  cent,  escaped  detection  until  1894,  perhaps  because  of 
its  great  inactivity,  as  all  of  the  many  attempts  to  make 
it  enter  into  combination  have  been  so  far  (1899)  without 
established  success.  Oxygen  is  the  most  universally  react- 
ive, forming  compounds  with  all  the  other  elements,  except 
fluorine,  argon,  and  helium. 

The  heat  disturbance  per  gram  of  element  in  combining  199 
with  oxygen  ranges  from  34,200  calories  for  hydrogen  in  the 
formation  of  water,  to  —1540  calories  for  nitrogen  in  the 
formation  of  nitric  oxide;  or  if  the  comparison  is  made 
per  combining  weight,  which  is  probably  more  suitable,  the 
values  are  143,900  calories  for  24  grams  of  magnesium, 
and  —21,600  calories  for  14  grams  of  nitrogen. 

1.  HYDROGEN 

Symbol  H.— Comb,  wt.  1 

History. — Hydrogen  was  studied  and  for  the  first  time  identified  by   200 
Cavendish  in  1766,  although  Paracelsus  in  the  sixteenth  century  noted 
the  production  of  an  inflammable  gas  by  the  action  of  acids  on  metals. 

In  1781  Cavendish  showed  that  it  is  a  constituent  of  water.     Its 
name  signifies  water-producer,  and  was  given  it  by  Lavoisier. 

Natural  occurrence.— It  is  found  uncombined,  but  only  in  201 
small  quantities,  in  volcanic  gases,  in  the  gas  from  oil  wells, 
and  sometimes  in  meteorites.  On  the  other  hand,  as  a  constit- 
uent, hydrogen  is  both  very  abundant  and  widely  distributed. 
It  forms  one  ninth  of  all  water,  and  is  contained  in  organic 
matter  of  both  plant  and  animal  origin,  and  also  in  all  acids. 


94          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

202  Preparation. — 1.  By  the  passage  of  the  electric  current 
through  slightly  acidulated  water  (electrolysis),  by  which 
hydrogen  and  oxygen  are  set  free. 


FIG.  2. — The  electrolysis  of  water.  Showing  how  the  current  from  the 
electric  battery  is  passed  through  acidulated  water,  and  the  gases  col- 
lected in<the  gasometric  tubes.  The  ratio  of  volumes  is  2:1. 

2.  By  the  action  of  some  dilute  acids  on  some  metals,  a 
salt  being  the  second  product.     Of  acids,  hydrochloric  and 
sulphuric  are  the  most  available,  and  for  the  metals,  zinc, 
iron,  magnesium,  and  aluminium  are  commonly  used. 

3.  By  the  action  of  sodium  or  potassium  hydroxide  in 
solution  on  some  metals,  usually  zinc  or  aluminium.     In 
this  reaction,  zinc  or  aluminium  oxide  is  produced   and 
combines   with    the    hydroxide,   forming   a    soluble   com- 
pound. 

4.  By  the  action  of  a  few  metals,  practically  sodium  and 
potassium,  on  water  at   ordinary  temperature,  the   metal 
being  oxidized  by  the  oxygen  of  the  water.     The  metallic 
oxide  in  turn  combines  with  water,  and  the  soluble  hydrox- 
ide is  formed. 

5.  By  the  action  of  some  metals,  for  example  iron,  at  a 
red  heat  on  water  vapor,  an  oxide  of  the  metal  being  the 
second  product. 


DESCRIPTION  OP  ELEMENTS  AND   COMPOUNDS      95 

6.  By  the  action  of  carbon  at  a  high  temperature,  white 
heat,  on  water  vapor.  The  carbon  is  oxidized  to  carbon 
monoxide,  a  gas,  so  that  a  mixture  of  this  substance  and 
hydrogen  is  obtained.  This  mixture  is  made  on  a  commer- 
cial scale  and  is  known  as  "  water-gas." 

These  reactions  are  expressed  in  equation  form  as  follows : 

1.  H20  =  2H  +  0 

2.  Zn  +  2HC1  =  2H  ^  ZnCl2 

3.  Zn  +  SNaOH  =  2H  +  Na2Zn02  (or  Na20,ZnO) 

4.  JSTa  +  H20  =  H  +  NaOH 

5.  3Fe  +  4H20  =  8H  +  Fe304 

6.  C  +  H20  =  2R  +  CO. 

Physical  properties. — Hydrogen  is  a  gas  without  color,  203 
taste,  or  odor.     The  odor  usually  noted  is  due  to  impurity 
coming  from  the  metal  or  the  acid.     It  is  the  lightest  of 
known  substances,  14.4  times  lighter  than  air.     One  liter 
of  it  weighs  0.0899  of  a  gram  at  0°  and  760  mm.     Being 
specifically  very  light,  it  also  possesses    high  diffusibiUtu  203/1 
—that  is,  the  power  of  mixing  with  other  gases,  and  of 
passing  through  a  porous  wall.     This  property  varies  in- 
versely as  the  square  root  of  the  density,  so  that  hydrogen 
diffuses  nearly  four  times  as  rapidly  as  air. 

It  is  but  slightly  soluble  in  water,  100  volumes  dissolving  204 
1.84  volumes  of  the  gas  at  760  mm.  and  20°  C. 

Occlusion. — Some  metals  show  the  property  of  absorbing 
hydrogen.  Conspicuous  for  this  is  palladium,  which  absorbs 
more  than  nine  hundred  times  its  volume  of  gas.  Platinum  205 
and  iron  show  the  property  in  less  degree.  The  hydrogen 
of  meteorites  is  thus  occluded  by  the  iron.  The  gas  absorbed 
is  given  up  again  at  a  high  temperature.  It  is  not  improb- 
able that  chemical  action  plays  some  part  in  occlusion. 

Liquefaction. — At  a  pressure  of  180  atmospheres  and  a  206 
temperature  of  —205°,  hydrogen  condenses  to  a  clear,  trans- 
parent liquid  whose  density  is  fourteen  times  less  than  that 
of  liquid  water,  and  whose  boiling  point,  under  atmospheric 


96          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

pressure  is,  —238°,  the  lowest  temperature  yet  reached 
(Dewar,  1898). 

207  Chemical  properties. — Hydrogen  has  no  action  on  litmus. 
It  burns  in  air  or  in  oxygen  with  a  pale-blue,  almost  in- 
visible flame,  forming  water,  and  liberating  34,200  calories 
per  gram,  which  is  niore  heat  than  any  other  substance 
gives  on  burning.      A  mixture  with  air  may  be  violently 
explosive,  as  already  stated.      At  a  high  temperature,  it 
reduces  many  metallic  oxides— that  is,  deprives  them  of 
oxygen — for  example,  copper,  silver,  and  even  iron  oxides. 
With  chlorine  it  combines  even  explosively,  and  it   also 
forms  compounds  with  bromine,  iodine,  carbon,  nitrogen, 
phosphorus,  sulphur,  and  the  metals,  potassium,  sodium, 
and  others. 

208  Nascent  state. — Hydrogen  and  also  other  substances  show, 
at  the  instant  of  liberation  from  a  compound,  a  higher  degree 
of  chemical  activity  than  after  the  separation  has  taken 
place.     This  is  called  the  nascent  state.    Nascent  hydrogen 
is  able  to  deprive  potassium  permanganate  of  a  portion  of  its 
oxygen,  a  power  which  hydrogen  in  mass  does  not  possess. 

208/2  As  a  theoretic  explanation  of  this  fact,  it  has  been  suggested  that  in 
the  nascent  state  the  substance  may  be  in  the  atomic  condition ;  the 
atoms,  not  having  come  together  into  molecules,  may  possess  more 
chemical  energy  than  after  they  are  united. 

209  Hydrogen  is  not  poisonous,  but  it  is  incapable  of  sustain- 
ing life.     It  may  be  inhaled  for  a  short  time,  and  in  this 
circumstance  it  gives  a  shrill  tone  to  the  voice. 

2.  LITHIUM 

Li.— 6.97 

210  History. — The  oxide  of  lithium  was  discovered  in   1817,  but  the 
element  was  not  separated  until  1855. 

211  Natural  occurrence. — It  is  not  found  free,  and  only  in 
small  quantities  as  a  constituent,  but  in  a  great  variety  of 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS      97 

compounds;  in  many  minerals,  in  particular  one  of  the 
varieties  of  mica ;  in  some  mineral  waters  and  in  the  sea ; 
in  some  soils  ;  in  some  plants — e.  g.,  tobacco,  beets,  sugar- 
cane ;  in  milk,  and  in  the  human  body ;  in  some  meteorites, 
and  in  the  atmosphere  of  the  sun. 

Preparation. — It  is  prepared  by  the  electrolysis  of  its  212 
fused  chloride. 

Properties. — It  is  a  metal  like  silver  in  color  and  luster,  213 
but  softer  than  lead.     With  a  specific  gravity  of  0.59,  it  is 
the  lightest  of  solids.     It  melts  at  180°. 

It  tarnishes  in  the  air  by  oxidation,  and  at  a  tempera-  214 
ture  above  180°  it  burns  brilliantly.  It  decomposes  water  at 
ordinary  temperature,  liberating  hydrogen  and  forming  the 
oxide,  which  is  Li20.  This,  in  turn,  combines  with  water, 
forming  -the  hydroxide,  LiOH,  which  is  soluble  and  is  a 
strong  base,  resembling  sodium  hydroxide. 

The  metal  combines  with  hydrogen,  carbon,  and  nitro- 
gen, forming  respectively  the  hydride,  LiH,  the  carbide, 
Li2C2 ,  and  the  nitride,  Li3N.  These  react  with  water  on 
contact,  forming  respectively  hydrogen,  acetylene,  C2H2, 
and  ammonia,  NH3.  Lithium  reacts  with  fluorine  and  with 
chlorine  violently,  and  the  metal,  and  its  oxide  and  its 
hydroxide,  react  with  hydrofluoric  acid  and  with  hydro- 
chloric acid,  in  each  case  forming  the  fluoride,  LiF,  or  the 
chloride,  LiCl.  Lithium  colors  the  Bunsen  flame  a  bright 
crimson. 

The  alkali  metals. — It  is  customary  and  convenient  to  215 
classify  in  one  group  or  family  those  metals  which  de- 
compose water  at  ordinary  temperature  and  form  soluble 
oxides  and  hydroxides,  which  act  as  strong  bases,  and  whose 
salts  are  generally  soluble.  They  are  called  the  alkalies, 
and  lithium,  sodium,  and  potassium  are  the  members  of  the 
group  which  are  described  in  this  course.  The  ammonium 
compounds  are  also  classified  with  these. 


98          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

3.  GLUCINUM:  or  BERYLLIUM 

Gl.  or  Be.— 9.0 

216  History. — The  oxide  of  glucinum   was  discovered  in  1798  in  the 
mineral,  beryl,  but  the  element  was  not  separated  until  1828,  and  then 
by  Wohler.     It  was  first  named  glucinum,  signifying  sweet,  from  the 
property  of  its  salts,  and  later  beryllium. 

217  Natural  occurrence. — It  is  not  found  free,  but  is  found 
in  some  minerals,  particularly  beryl,  of  which  emerald  and 
aquamarine  are  varieties.      In  these  it  is  combined  with 
oxygen,  silicon,  and  aluminium. 

218  Preparation. — It  is  obtained  by  heating  its  chloride  with 
sodium. 

219  Properties. — It  is  a  white  metal.     Its  melting  point  is 
lower  than  that  of  silver.     Its  specific  gravity  is  1.85  at  20° 
(Ramsay).     When  in  compact  condition,  it  oxidizes  only  su- 
perficially in  the  heat  of  the  blowpipe.     If  finely  divided, 
it  burns  brilliantly  when  heated  in  the  air.     It  does  not 
decompose  water  below  100°.     Its  oxide  is  G10,  a  white 
powder,  insoluble  in  water,  which,  however,  forms  a  hy- 
droxide with  water,  G102H2.      The  latter  is  insoluble  in 
water,  and  acts  as  a  base  primarily.     The  metal,  the  oxide, 
and  the  hydroxide  react  with  hydrochloric  acid,  forming 
the  soluble  chloride,  G1C12.     They  also  dissolve  in  sodium 
and  potassium  hydroxides,  forming  glucinates,  compounds 
in  which  glucinum  oxide  seems  to  act  as  acid  to  the  alkali 
base.     Glucinum  forms  a  hydride   (G1H?),  and  a  carbide 

(GW). 

4.  BORON 

B.-10.86 

220  History. —Boron  was  first  separated  as  an  element  about  1808  by 
Gay-Lussac,  Thenard,  and   Sir   Humphry  Davy,   but   its  compound, 
borax,  was  known  many  years  earlier. 

221  Natural  occurrence, — It  has  not  been  found  uncombined, 
but  its  oxide,  combined  with  water— that  is,  boric  acid— oc- 


DESCRIPTION  OF  ELEMENTS  AND   COMPOUNDS      99 

curs  in  the  water  of  some  volcanic  regions,  notably  in  Tus- 
cany, also  as  a  mineral ;  and  the  sodium  salt  of  this  acid, 
known  as  borax,  is  found  abundantly  in  California,  and  is  a 
familiar  article  of  commerce. 

Preparation, — Boron   is  best    prepared    by  heating  its  222 
oxide,  B203,  with    magnesium,  which   combines  with   the 
oxygen  and  liberates  the  boron. 

Properties  (according   to   Moissan,  1895).* — Thus  pre-  223 
pared,  it  is  a  brown  amorphous  powder,  of  neither  taste 
nor  odor,  insoluble  in  all  ordinary  solvents,  and  infusible, 
but  probably  volatile  without  fusion  in  the  electric  arc. 
Its  specific  gravity  is  2.45. 

It  forms  with  hydrogen  the  compound  BH3.f  Heated  224 
in  air  to  700°,  it  burns  readily,  forming  the  oxide  B203, 
and  in  oxygen  it  burns  with  intense  brilliancy.  It  com- 
bines directly  with  fluorine,  with  chlorine,  and  with  bro- 
mine, forming  BF3,  BC13,  and  BBr3 ;  with  carbon,  B6C  and 
B202 ;  with  sulphur,  B2S3 ;  and  with  some  metals — e.  g.,  iron, 
BFe,  and  aluminium  and  magnesium.  At  1230°  it  combines 
with  nitrogen,  forming  BN.  Above  red  heat  it  decomposes 
water  violently.  It  also  removes  oxygen  from  many  metal- 
lic oxides.  Indeed,  it  is  a  most  active  reducing  agent. 

Boron  oxide,  B203,  is  the  only  compound  with  oxygen.  It  225 
is  formed  by  direct  union  with  oxygen,  and  also  by  driving 
off  the  water  of  boric  acid  at  a  red  heat.  It  melts  to  a 
glasslike  mass,  and  volatilizes  only  at  the  highest  tempera- 
ture. It  dissolves  in  water,  at  the  same  time  combining 
with  water,  forming  a  hydroxide  commonly  called  boric 
acid.  This  may  be  crystallized  from  water  in  white  shining 
scales.  It  is  also  liberated  from  the  borates  by  sulphuric 
or  hydrochloric  acid.  It  is  soluble  in  alcohol,  and  imparts  226 
to  the  alcohol  flame  a  characteristic  green  color.  This  is  a 
common  test  for  its  identification. 


*  Annales  de  Chemie  et  de  Physique  (7),  vi,  1895. 
t  Sabatier,  Comptes  rendus,  1891. 

8 


100        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

227  Boron  oxide  combines  with  water  in  three  proportions, 
forming  acids,  thus : 

B203  +  3H20  =  H6B206  =  2H3B03,  named  orthoboric  acid. 
B203  +  H20  —  H2B204  =  2HB02,  named  metaboric  acid. 
2B203  +  H20  =  H2B407,  named  tetra  or  pyroboric  acid. 

Borax  is  the  sodium  salt  of  the  pyroboric  acid,  Na2B407, 
crystallizing  with   10H20,  and  showing   a  slight  alkaline 

228  reaction.     The  fused  salt,  and  the  boric  oxide  itself,  dis- 
solve many  of  the  metallic  oxides,  in  many  instances  form- 
ing transparent  glasslike  substances  of  characteristic  colors. 
These  are  used  for  identification  in  the  borax-bead  tests. 
Borax  is  used  also  for  cleaning  metallic  surfaces  prepara- 
tory to  soldering,  for  glazing  porcelain,  in  the  making  of 
glass  and  of  soap,  also  as  a  drug,  and  as  an  antiseptic — that 
is,  as  a  preventive  of  putrefaction  and  fermentation. 

Boron  oxide  in  the  compounds  mentioned  and  in  others 
clearly  acts  as  an  acid-forming  oxide.  But  it  seems  to  be 
capable  of  acting  also  as  a  feeble  base.  It  reacts  with  hydro- 
fluoric acid,  forming  a  fluoride,  as  do  metallic  oxides,  although 
this  compound  is  a  gas  and  readily  decomposed  by  water : 

B203  +  6HF  =  2BF3  +  3H20. 

It  combines  with  phosphoric  acid,  H3P04,  forming  a  phos- 
phate, BP04,  in  which  the  boron  apparently  acts  as  a  base. 


5.  CARBON 

C.— 11.91 

234  Uncombined  carbon  exists  in  three  allotropic  forms — 
diamond,  graphite,  and  amorphous  carbon  of  which  char- 
coal is  one  variety. 

Diamond 

235  History. — Diamond,  the  transparent  crystallized  form  of 
carbon,  has  been  known  and  prized  as  a  gem  for  ages.     It 


Of     FMJ-  Wi 

„    UNIVERSITY 

DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   101  / 

^^.LIFO  H  *•  \  .^ 

was  at  one  time  regarded  as  a  variety  of  rock  crystal 
(silica).  Sir  Isaac  Newton  surmised  that  it  might  be  com- 
bustible because  of  its  high  refractive  power,  like  that  of 
turpentine  and  other  substances  which  were  known  to 
burn.  In  1695  two  Italians  proved  the  correctness  of  this 
suggestion  by  burning  a  diamond  in  the  focus  of  a  power- 
ful burning-glass.  Later,  about  1766,  Dorcet  showed  that 
when  heated  in  a  hermetically  sealed  vessel  the  diamond 
was  unchanged.  Then  Lavoisier,  in  connection  with  his 
famous  investigation  of  combustion,  burned  the  diamond 
in  a  closed  vessel  with  air  and  proved  the  formation  of 
carbon  dioxide.  Then,  by  the  work  of  several  investi- 
gators, between  1796  and  1800,  it  was  proved  that  equal 
weights  of  charcoal,  graphite,  and  diamond  gave  equal 
weights  of  carbon  dioxide.  Finally,  Sir  Humphry  Davy, 
in  1814,  using  the  same  burning-glass  that  was  used  by 
the  Italians  in  1695,  showed  that  no  water  was  produced 
in  burning  diamond,  and  therefore  that  this  substance 
contains  no  hydrogen.  He  went  still  further,  and,  com- 
bining with  lime  the  carbon  dioxide  made  by  burning  dia- 
mond, he  produced  calcium  carbonate,  which  in  turn 
he  reduced  by  heating  with  potassium.  This  yielded 
him  a  black  powder  which  burned  like  ordinary  charcoal. 
(History  according  to  Roscoe.)  Thus  the  evidence  be- 
came complete  that  diamond  is  simply  pure  crystallized 
carbon. 

Diamonds  have  been  found  in  the  East  Indies,  since  236 
1727  in  Brazil,  and  since  1867  in  South  Africa ;  to  a  less 
extent  elsewhere.     Its  presence  in  a  meteorite  has  been 
noted. 

Properties.— The  diamond  is  a  natural  crystal,  which,  237 
however,  is  cut  and  polished  to  serve  as  a  gem.  It  is  trans- 
parent, sometimes  colorless,  sometimes  tinted  green,  brown, 
or  yellow,  sometimes  black.  Its  luster  and  high  refractive 
power  give  it  brilliancy  as  a  gem.  In  hardness  it  is  not  ex- 
ceeded by  any  known  substance,  and  is  equaled  by  only  one 


102        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

or  two.     Its  specific  gravity  is  3.5  at  least.     It  is  a  poor 
conductor  of  heat  and  electricity. 

238  It  may  be  heated  in  hydrogen  to  1,200°,  white  heat, 
without  change ;  but  when  thus  heated  in  the  electric  arc 
it  swells,  and  becomes  black  like  coke  or  graphite.     When 
heated  in  oxygen  to  700°  or  800°  it  burns,  leaving  only  a 
minute  ash.     It  reacts  with  no  substances  at  ordinary  tem- 
perature, and  even  at  high  temperature  with  only  a  few. 
Heated  to  1,000°,  it  is  acted  upon  by  sulphur,  giving  carbon 
disulphide ;  also  by  sodium  or  potassium  carbonate,  giving 
carbon  monoxide.     Melted  iron  and  melted  platinum  dis- 
solve it  and  combine  with  it,  and  on  cooling  give  it  up  as 
graphite  (according  to  Moissan,  1896). 

239  TTses. — Some  of  the  most  famous  diamonds  of  the  world  are  in  the 
possession  of  states  or  sovereigns.     The  Regent  diamond  weighs  136 
carats,  or  about  27.9  grams  (a  carat  equals  0.205  of  a  gram),  and  is  valued 
at  $625,000.     Diamonds  of  inferior  quality  are  used  to  cut  and  polish 
diamonds  and  other  gems,  and  as  points  of  tools  for  boring  rocks  and 
for  cutting  glass. 

240  Carbonado  and  anthracitic  diamond  are  forms  of  impure 
carbon,  approaching  the  diamond  in  properties,  but  of  less 
density  and  hardness  than  the  true  diamond. 

241  Artificial  diamond. — Of  the  many  who  have  attempted 
to  prepare  the  real  diamond  artificially,  Moissan  was  the 
first  to  succeed  and  to  prove  his  success  beyond  question. 
The  account  of  this  work  was  published  in  1896.     His  pro- 
cedure was  to  saturate  molten  iron  (silver  also  was  used  in 
place  of  iron)  with  pure  carbon  in  the  electric  furnace  at 
the  enormous  temperature  of  about  3,500°,  which  greatly 
increases  the  solvent  power.     This  mass  was  then  suddenly 
cooled  by  plunging  it  into  water,  or  sometimes  into  melted 

-  lead  whose  temperature  was  about  325°.  Under  these  con- 
ditions a  solid  crust  is  formed  while  the  interior  is  still 
molten,  and  as  iron  expands  on  solidifying,  the  liquid  por- 
tion is  thus  put  under  great  pressure.  When  sufficiently 
cool,  the  metal  and  the  excess  of  carbon  (now  graphite)  were 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   103 

dissolved  by  reagents,  and  minute  crystals  or  crystalline 
fragments  were  obtained,  which  were  sometimes  black, 
sometimes  transparent,  had  the  hardness  and  specific  grav- 
ity of  the  diamond,  and  consisted  of  pure  carbon,  in  fact 
were  minute  but  real  diamonds.  The  great  pressure  was 
found  to  be  an  essential  condition,  and  without  it  the  car- 
bon appeared  simply  as  graphite. 

One  of  his  samples  measured  0.$7  mm.,  and  among  them  242 
were  reproduced  many  of  the  peculiar  features  seen  in 
natural  diamonds.     The  remarkable  results  of  Moissan's  ex- 


FIG.  3. — One  form  of  the  electric  furnace  for  research  work  ;  e  and  e1,  the 
poles  by  which  the  current  enters  and  leaves ;  6,  the  crucible  in  which 
the  material  is  heated  by  the  arc  ;  the  sides  are  figured  open  in  order 
to  show  the  arrangement. 

periments  give  much  force  to  his  suggestion  that  the  natural 
diamond  has  probably  been  formed  in  the  deeper  layers  of 
the  earth's  crust,  where  enormous  pressure  exists,  and  that 
it  is  not  unlikely  that  iron  may  have  been  the  solvent.  In- 
deed, minute  transparent  diamonds  have  been  found  in  the 
midst  of  meteoric  masses  of  iron. 


104        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

4 

Graphite 

243  Graphite,  the  second  allotropic  form  of  carbon,  called 
also  plumbago  and  Uack  lead,  is  found  in  considerable  quan- 
tities and  in  many  places,  notably  in  England,  Bohemia, 
Siberia,  Ceylon,  California,  Massachusetts,  New  York,  and 
Michigan.     Its  presence  in  meteoric  iron  has  been  noted. 

244  It  exists  in  crystallized  condition.     In  color  it  is  black 
or  grayish  black,  and  sometimes  of  almost  metallic  luster. 
It  is  so  soft  that  it  makes  a  black  mark  on  paper  and  leaves 
a  stain  on  the  finger,  and  it  is  soapy  to  the  touch.     It  differs 
from  the  diamond  in  lower  specific  gravity,  about  2.0-2.25, 
and  in  igniting  in  oxygen  below  700°;  also  in  yielding  to 
oxidation  by  a  mixture  of  strong  nitric  acid  and  potassium 
chlorate,  whereby  a   colored,  green  or  yellow,  crystalline 
oxide  is  obtained.     It  is  also  a  good  conductor  of  heat  and 
of  electricity.     At  low-red  heat  it  does  not  decompose  water 
nor  oxidize  in  air.     Natural  graphite  leaves  more  ash  than 
diamond. 

245  It  is  made  artificially  by  heating  diamond,  or  the  many 
varieties  of  charcoal,  to  the  high  temperature  of  the  electric 
arc ;    also    by  dissolving  carbon   in   many  of  the  metals, 
melted  at  a  high  temperature.     When  the  metal  cools,  the 
graphite  separates  in  crystals. 

246  Uses. — The  substance  finds  use  as  material  for  crucibles  in  which 
metals  are  melted,  both  on  a  large  and  a  small  scale ;  as  material  for 
which  the  so-called  lead  of  pencils  is  made,  whence  its  name  signifying 
to  write;  as  conducting  material  in  the  process  of  electroplating;  and 
as  lubricant. 

Carbon  as  Constituent 

247  Besides  diamond  and  graphite,  the  native  forms  of  the 
element,  carbon  as  a  constituent  is  found  in  the  air  and  in 
natural  waters  as  carbon  dioxide;  in  all  the   carbonates, 
such  as   marble,  limestone,  chalk ;  in   petroleum  and  'in 
"  natural  gas  " ;  as  the  fundamental  constituent  of  all  plant 
and  animal  structures ;  and  in  all  varieties  of  coal. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   105 

Amorphous  Carbon 

Preparation. — From  the  fully  oxidized  compounds  of  248 
carbon — that  is,  carbon  dioxide  and  the  carbonates — carbon 
can  be  obtained  only  by  removing  the  oxygen  with  which  it 
is  combined.  This  may  be  done  by  heating  with  such  sub- 
stances as  boron  and  magnesium.  From  substances  of 
plant  and  of  animal  origin,  in  which  it  is  combined  with 
hydrogen,  and  often  with  oxygen  and  nitrogen,  but  in  which 
it  is  not  fully  oxidized,  it  is  obtained  generally  by  charring 
or  by  dry  distillation — that  is,  by  heating  without  sufficient 
air  to  cause  complete  combustion.  The  constituent  hydro-  249 
gen  burns  the  more  easily ;  therefore  the  carbon  predomi- 
nates in  the  residue.  The  varieties  of  carbon  thus  obtained 
depend  on  the  various  sources  and  the  methods  of  making. 
They  are  all  quite  impure  as  commercial  articles,  but  they  are 
alike  in.  being  soft,  amorphous,  black  or  brown,  of  specific 
gravity  less  than  2.0 ;  easily  oxidized  by  nitric  and  chromic 
acids ;  and  some  of  them  take  fire  in  oxygen  as  low  as  375°. 

Lampblack  is  one  of  the  purest  varieties.     It  is  the  black  250 
deposit  familiarly  known  as  soot,  from  the  flame  of  carbon- 
containing   fuel,  made   smoky  by  incomplete  combustion. 
It  is  used  in  making  inks  and  paints. 

Qus_cjir^on  is  deposited  from  the  gases  in  the  retorts  in  251 
which  illuminating  gas  is  made.     It  is  harder  and  denser, 
and,  being  a  good  conductor,  has  been  used  in  making 
battery  plates  and  the  poles  of  electric  lamps. 

Bone  Nock  or  anj'mal  char  coal  is  the  residue  obtained  252 
by  charring  bone,  blood,  and  other  refuse  of  animal  origin. 
It  is  very  porous  and  absorptive,  and  is  used  largely  to 
decolorize  sirups  in  sugar  refining. 

CoJ^is  the  solid  residue  from  the  distillation  of  coal  253 
and  is  used  extensively  as  fuel,  especially  in  obtaining  metals 
from  their  oxides. 

Wood  charcoal  is  the  solid  residue  from  the  distillation  254 
of  wood.     When  wood  is  heated  to  high  temperature  with 


106        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

little  or  no  air  present,  water  is  eliminated,  also  a  gaseous 
mixture  which  burns  with  luminous  flame  and  contains  car- 
bon and  hydrogen ;  a  liquid  also  is  obtained  which  has  acid 
reaction,  and  contains  creosote  and  other  tarlike  substances 
of  which  carbon  is  a  constituent.  The  greater  part  of  the 
carbon,  a  little  of  the  hydrogen,  and  all  of  the  ash  are  left 
254/1  in  the  solid  residue,  which  is  charcoal.  This  retains,  more 
or  less,  the  structure  of  the  wood ;  is  black  or  brown,  soft, 
brittle,  and  very  porous  and  absorptive.  It  floats  on  water 
only  until  the  air  is  expelled  from  its  pores.  Its  properties 
vary  considerably  with  the  kind  of  wood  and  the  tempera- 
ture of  distillation.  It  is  able  to  absorb  from  90  to  170 

255  times    its    own    volume    of    ammonia   gas,  about    50  vol- 
umes  of   hydrogen    sulphide,  from  10   to    18  volumes  of 
oxygen,  etc.     This  property  leads  to  its  use  for  the  pur- 
pose of  absorbing  the  offensive  and  harmful  gases  which 
accompany  putrefaction,  also  to  purify  the  air  in  the  sick- 
room, etc.      By  virtue  of   the  same  property,  it  removes 

255/1  many  substances  from  solution,  and  hence  its  extensive 
use  as  filtering  material — e.  g.,  to  remove  the  coloring 
matter  from  sirups  on  a  large  scale ;  also,  to  filter  water 
for  drinking.  In  some  instances  it  seems  to  absorb  phys- 
ically, and  the  substances  may  be  recovered  from  the 
charcoal ;  in  others  it  brings  about  chemical  changes  within 
its  pores,  especially  oxidation.  Thus,  when  used  as  filter- 
ing material,  it  loses  its  effectiveness  in  time,  and  this  may 
be  restored  by  exposure  to  air,  which  renews  its  supply  of 
absorbed  oxygen. 

Common  Properties 

256  It  ?s  seen,  therefore,  that  the  element  carbon,  as  to  many 
of  its  properties,  varies  in  a  most  remarkable  manner  in  its 
different  conditions.     In  all  its  forms  it  was  regarded  as 
entirely  infusible   and  non-volatile   until  Moissan  showed 
that  at  the  highest  temperature  of  the   electric  furnace 
(3,600°)  it  volatilizes  without  melting,  and  condenses  as 


JOSEPH   BLACK 

B.  Bordeaux,  1728.     D.  Edinburgh,  1799. 
(See  Nos   259,  577.) 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    107 

graphite.  It  is  insoluble  in  all  ordinary  solvents,  but  dis- 
solves in  many  of  the  metals  which  melt  at  high  tempera- 
ture. 

In  its  chemical  reactions  also  carbon  is  most  remarkable.  257 
At  ordinary  temperature  it  is  almost  completely  inactive, 
although  in  amorphous  condition  it  does  yield  to  powerful 
oxidizing  agents  below  100°.  It  must  be  heated  to  several 
hundred  degrees  before  it  combines  with  the  oxygen  of  air, 
but  when  heated  it  is  able  to  take  oxygen  from  many  com- 
pounds. This  leads  to  the  use  of  charcoal  and  coke  on  an 
enormous  scale  in  the  industrial  processes  of  obtaining  the 
metals  from  their  native  oxides  (i.  e.,  metallurgy). 

In  the  high  temperature  of  the  electric  arc,  carbon  com-  258 
bines  directly  with  hydrogen,  forming  acetylene,  C2H2.  It 
forms  innumerable  other  compounds  with  hydrogen,  but 
not  by  direct  action  between  the  two  elements.  It  also 
combines  at  high  temperature  with  lithium,  forming  a 
crystallizable  compound,  Li2C2 ;  likewise  with  many  other 
metals — e.  g.,  sodium,  potassium,  magnesium,  and  calcium, 
forming  also  carbides  ;  with  boron,  forming  B6C,  crystalline, 
and  rivaling  the  diamond  in  hardness ;  with  nitrogen,  form- 
ing the  intensely  poisonous  cyanogen,  C2N2 ;  with  fluorine ; 
with  chlorine,  CC14;  with  silicon,  forming  carborundum, 
CSi,  very  hard  and  used  like  emery  in  grinding  and  polish- 
ing ;  and  with  sulphur,  CS2. 

5a.  Carbon  Dioxide,  C02 

History.— Van  Helmont  (1577-1644)  noted  that  a  substance  which  259 
he  named  "gas  Sylvester"  was  produced  by  fermentation,  by  decay, 
and  by  combustion,  and  was  found  in  certain  natural  caves.  He  ob- 
tained it  by  the  action  of  acids  on  carbonates,  and  observed  that  it  suf- 
focated animals  and  extinguished  flame.  Black  (1755)  called  it  "fixed 
air."  Bergmann  studied  it  in  1774,  and  named  it  "acid  of  air."  But 
Lavoisier  first  explained  its  chemical  relationship  (Roscoe). 

Natural  occurrence. — It  is  a  normal   constituent  of  the  260 
atmosphere  to  the  extent  of  about  4  volumes  in  10,000.     It 


108        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

is  a  product  of  ordinary  combustion,  of  the  respiration  of 
animals,  of  fermentations,  and  of  organic  decay.  It  issues 
from  the  earth  in  some  volcanic  regions,  and  is  dissolved 
in  most  natural  waters.  As  a  constituent  of  carbonates  it 
occurs  abundantly  in  the  soil  and  in  extensive  layers  of  the 
earth's  crust. 

261  Preparation. — It  is  commonly  prepared  by  the  action  of 
acids  on  carbonates,  or  by  decomposing  calcium  carbonate 
by  heat,  or  by  burning  carbonaceous  matter. 

262  Properties. — It  is  a  gas  at  ordinary  temperature,  without 
color,  and  with  little,  if  any,  odor.     It  is  one  and  a  half 
times  heavier  than  air,  and  twenty-two  times  heavier  than 
hydrogen.     At  normal  pressure  and  at  20°,  100  volumes  of 
water  dissolve  about  90  volumes  of  the  gas.     The  quantity 
dissolved  is  greatly  increased  by  pressure,  but  when  the 
pressure  is  removed  the  gas  escapes  with  effervescence.     It 
condenses  at  10°,  under  a  pressure  of  about  36  atmospheres, 
to  a  clear,  colorless  liquid,  whose  boiling  point  is  —78°, 
and  freezing  point  nearly  the  same.     It  freezes  by  its  own 
evaporation  to  a  white,  snowlike  solid.     Liquid  carbon  di- 
oxide, stored  in  strong  iron  cylinders,  has  become  a  com- 
mercial article. 

263  Carbon  dioxide  is  not  combustible,  and  it  extinguishes 
all  ordinary  combustion  and  destroys  animal  life.     A  few 
substances — boron,  sodium,   potassium,  and   magnesium — 
when  heated,  burn  in  it,  depriving  it  of  its  oxygen.     Ked- 
hot  carbon  also  decomposes  it,  forming  carbon  monoxide, 
and  it  is  partly  decomposed  into  this  substance  and  oxygen 
by  a  temperature  of  1,300°.     A  candle  ceases  to  burn  in 
air  containing  4  per  cent  of  carbon  dioxide,  although  the 
oxygen  is   far   from  exhausted.     An  animal   can  tolerate 
such  air  for  only  a  short  time ;  hence  the  method  of  test- 
ing by  a  lighted  candle  the  air  of  wells,  caves,  mines,  or 
similar  places  where  the  gas  may  accumulate  by  reason  of 
its  high  specific  gravity.     Fatal  accidents  have  happened 
from   failure   to   take    precautions    before    entering   such 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   109 

places.  Miners,  who  have  frequently  to  encounter  it,  call 
it  "  choke  damp."  Air  containing  so  little  as  0.2  per  cent 
is  said  to  have  injurious  effect  if  long  respired. 

In  dissolving  in  water  the  gas  probably  combines  with  264 
it  to  slight  extent,  forming  dilute  carbonic  acid,  since  the 
solution  feebly  reddens  litmus,  whereas  the  dry  gas  does 
not.  The  acid  is  very  unstable,  however,  easily  changing 
into  the  original  constituents ;  but  if  a  soluble  base  is  pres- 
ent the  salt  is  formed,  and  this  is  quite  stable.  The  salts 
are  called  carbonates,  and  their  composition  implies  an  acid  265 
of  the  formula  H2C03.  Those  of  the  alkali  bases,  like 
sodium  carbonate,  are  soluble.  The  others  are  generally 
insoluble.  Upon  this  fact  depends  the  usual  test  for  car- 
bon dioxide,  namely,  the  turbidity  produced  in  lime-water 
(calcium  hydroxide). 

Relation  to  life. — In  relation  to  living  things,  carbon  266 
dioxide  plays  a  most  important  part.  As  has  been  already 
stated,  carbon  is  the  fundamental  element  of  both  the  plant 
and  the  animal  organism.  The  carbon  dioxide  of  the  at- 
mosphere constitutes  an  essential  food  of  plants.  From 
this  and  water  it  builds  up  much  the  greater  portion  of  its 
substance.  Absorbing  the  gas  by  the  extensive  surface  of 
its  leaves  and  other  green  parts,  and  aided  by  the  energy  of 
sunlight,  associated  in  some  way  with  the  green  coloring 
matter  of  the  leaves  (called  chlorophyll],  the  plant  is  able  to 
remove  a  part;  of  the  oxygen,  rejects  it,  as  it  were,  and 
passes  back  to  the  atmosphere  a  quantity  of  it  nearly  equal 
to  that  contained  in  the  carbon  dioxide  absorbed.  From  the 
residue  it  builds  up  the  wood,  starch,  sugar,  and  many  other  267 
substances  which  constitute  its  entirety.  Upon  these,  or  a 
part  of  them,  the  animal  depends  for  his  food,  consuming 
some,  such  as  starch  and  sugar,  and  from  them  not  only 
building  his  body  substance,  but  deriving Jnsjmergy- by  the . 
chemical  change^_jsdiich^hey-ftndergo.  These  changes  re- 
sult ultimately  in  the  complete  oxidation  of  a  part  of  the 
carbon  to  carbon  dioxide  and  the  rejection  of  this  from  the 


HO        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

lungs  as  a  waste  product,  which  is-  thus  returned  to  the  at- 
mosphere to  serve  again  as  food  for  the  plant.     In  addition 

268  to  this,  man  utilizes  the  deoxidized  carbon  of  the  plant  in 
the  form  of  wood,  or,  as  will  be  seen  later,  in  the  form  of 
coal,  as  the  chief,  practically  the   only,  source  of  artificial 
heat,  and  hence  of  the  mechanical  energy  which  is  depend- 
ent on  it.     One  of  the  marvelously  delicate  adjustments  of 
nature  is  seen  in  the  fact  that  the  proportion  of  carbon  diox- 
ide in  the  atmosphere,  considering  it  as  a  whole,  has  not  ap- 
preciably changed  within  the  history  of  observation,  and  prob- 
ably not  during  the  existence  of  the  human  race ;  and  this, 
in  spite  of  the  immense  quantities  of  the  substance  thrown 
into  the  air  by  respiration,  by  combustion,  and  by  decay,  and 
drawn  out  of  it  and  stored  up  in  the  enormous  mass  of  plant 
products. 

5b.  TJie  Carbonates 

269  The   carbonates   occur   frequently   and    abundantly  as 
minerals — e.  g.,  iron  carbonate,  magnesium  carbonate,  and, 
most  abundant  of  all,  calcium  carbonate  in  its  several  varie- 
ties, namely,  chalk,  limestone,  marble,  and  calcite.     Sodium 
carbonate  and  potassium  carbonate  are  manufactured  and 
used  in  large  quantities. 

270  The  carbonates  in  some  instances  are  formed  by  the 
combination  on  contact  of  carbon  dioxide  and  basic  hydrox- 
ides.    The  formation  of  sodium  carbonate  and  calcium  car- 
bonate in  this  way  has  already  been  cited.     Calcium  oxide, 
CaO,  and  one  or  two  other  oxides  combine  directly  with 
carbon  dioxide,  liberating  much  heat.     Non-alkali  carbon- 
ates, being  insoluble,  are  precipitated,  if  they  form  at  all,  by 
mixing  solutions  of  non-alkali  salts  and  alkali  carbonates. 
Some  bases,  however — e.  g.,  aluminium  hydroxide — do  not 
combine  with  carbonic  acid  in  the  presence  of  water. 

271  There  are  two  types  of  carbonates— those  in  which  the 
metal  has  displaced  the  whole  of  the  acid  hydrogen,  and 
those  in  which  only  one  half  is  displaced.     The  first  are 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    HI 


the  normal^  the  second,  the  acid  carbonates.  Of  the  first 
type  are  sodium  carbonate,  Na2C03,  and  calcium  carbon- 
ate, CaC03  ;  of  the  second  is  sodium  acid  carbonate,  or  bi- 
carbonate, NaHC03.  The  acid  carbonates  of  the  alkalies 
only  are  well  defined.  The  acid  carbonates  of  calcium, 
magnesium,  iron,  and  others  are  supposed  to  be  formed 
when  the  normal  carbonates  are  dissolved  by  excess  of  car- 
bon dioxide,  but  they  decompose  so  easily  that  they  can 
not  be  obtained  out  of  solution,  and  heating  the  latter 
causes  the  precipitation  of  the  normal  carbonates. 

5c.  Carbon  Monoxide,  CO 

This,  the  second  of  the  two  oxides  of  carbon,  is  produced  272 
in  circumstances  which  do  not  permit  the  complete  oxidation 
of  carbon—  e.  g.,  insufficiency  of  oxygen  ;  also  when  carbon 
dioxide  passes  over  red-hot  carbon  or  metals.     It  is  a  gas    « 
without  odor  or  color.    Its  specific  gravity  (H  =  1)  is  13.93, 
nearly  the  same  as  air.     One  hundred  volumes  of  water  dis- 
solve only  about  two  of  the  gas.     Under  great  pressure  and 
low  temperature  it  condenses  to  a  liquid  which  boils  at 
—  190°  and  freezes   to  a  white  solid  at  —199°.     It  burns 
with  a  pale-blue  flame  to  carbon  dioxide.     The  flickering  273 
that  is  frequently  seen  over  a  bed  of  glowing 
o  this  substance,  formed  from  the  dioxide.  _  . 


_ 

wEIch_passes  ujjward  through  the  hot  mass,  is  deoxidized, 
and  burns  as  the  monoxide  when  it  comes  to  abundant  air. 
The  monoxide  has  no  action  on  litmus,  and  forms  no  acid 
with  water.  It  is  intensely  poisonous,  combining  with  one 
of  the  constituents  of  the  blood,  and  fatally  modifying  its 
normal  action.  The  not  infrequent  deaths  through  expo- 
sure to  the  gas  from  coal  stoves  and  furnaces  are  due  to  this 
substance,  which  is  the  more  dangerous  from  the  fact  that 
it  has  no  odor  and  its  stupefying  effects  give  no  alarm. 
One  per  cent  in  the  air  may  cause  death  (Parkes).  It  is 
present  in  common  illuminating  gas. 


112        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

5d.  The  Hydrocarbons 

274  This  is  the  name  applied  to  the  compounds  of  carbon 
and  hydrogen.  They  are  many  in  number  and  varied  in 
kind,  and  reveal  another  remarkable  property  of  this  ele- 
ment, carbon. 

2  75  Methane  is  the  simplest  of  the  group ;  its  formula  is 
CH4.  It  occurs,  first,  as  a  product  of  the  decay  of  plant  sub- 
stances— for  example,  in  stagnant  water  and  marshes,  where 
bubbles  of  gas  may  be  seen  coming  to  the  surface,  or  may 
be  caused  to  rise  in  quantity  by  stirring  the  sediment  at 
the  bottom  (whence  its  name  "  marsh-gas " )  ;  second,  in 
coal  mines, .where  it  is  known  as  "  fire-damp,"  and  causes 
many  terrible  explosions ;  third,  associated  with  petroleum, 
and  as  the  chief  constituent  of  the  so-called  "  natural  gas." 
As  an  artificial  product,  it  is  the  larger  part  of  the  gas  pro- 
duced in  the  distillation  of  wood  and  of  coal — i.  e.,  illumi- 
nating gas.  For  laboratory  purposes  it  is  conveniently 

276  prepared  by  the  dry  distillation  of   sodium  acetate  mixed 
with  a  strong  base  such  as  lime.     It  is  formed  also  by  the 
action  of  water  or  acids  on  some  of  the  metallic  carbides,  at 
ordinary  temperature ;  for  example,  aluminium  carbide,  thus, 

C3A14  +  12H20  =  3CH4  +  2A12(OH)6 ; 

also  by  the  reaction  which  is  expressed  in  the  following 
equation : 

2H2S  +  CS2  +  8Cu  (red  hot)  =  CH4  +  4Cu2S. 

277  Methane  is  a  gas  without  color  or  odor,  and  nearly  in- 
soluble in  water.     Its  specific  gravity  is  7.95  (H  =  1).     It 
condenses  to  a  liquid  which  boils  at  — 164°,  and  solidifies 
at  about  —186°.    It  burns  with  a  pale,  almost  non-luminous 
flame  to  carbon  dioxide  and  water. 

278  Closely  allied  with   methane  are  ethane,  propane,  and 
butane,  which  have  the  formulas,  respectively,  C2H6,  C3H8, 
and  C4H10.     In  composition  they  differ  from  each  other  by 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   113 

the  constant  difference  CH2.  Substances  thus  differing  in 
composition  and  possessing  a  family  or  group  resemblance 
in  properties  are  said  to  be  homologous,  and  the  series  is 
called  a  homologous  series.  The  one  of  which  methane  is 
the  first  member  is  called  the  paraffin  series.  They  may  be 
represented  by  the  general  formula  CnH(2n+  2).  One  is  known 
in  which  n  =  60.  As  the  proportion  of  carbon  increases 
beyond  n  =  4  they  become  liquids,  and  finally  solids  at 
ordinary  temperature. 

Ethylene,  C2H4,  is  the  first  member  of  a  second  series  of  279 
hydrocarbons  known  as  the  ethylene  or  olefin  series.  It, 
too,  is  a  product  in  the  dry  distillation  of  wood  and  coal. 
It  is  also  formed(by  the  action  of  acids  on  some  of  the 
metallic  carbides,  and  in  the  laboratory  usually  by  heating 
a  mixture  of  strong  sulphuric  acid  and  alcohol.  It  is  a 
colorless  gas,  almost  insoluble,  condensable  to  a  liquid  which 
boils  at  —105°.  It  burns  with  a  bright  flame,  and  is  the 
chief  light-giving  constituent  of  illuminating  gas.  Others 
of  the  series  are  propylene,  C3H6,  and  butylene,  C4H8.  Their 
general  formula  is  CnHsn,  and  the  increment  of  composition 
is  CH2,  as  in  the  paraffins. 

Acetylene,  C2H2,  is  the  first  member  of  the  third  series,  280 
and  is  of  special  interest.  Reference  has  already  been 
made  to  the  fact  that  this  substance  is  produced  by  the 
direct  union  of  the  elements  at  the  temperature  of  the  elec- 
tric arc,  and  that  it  is  endothermic  (see  Nos.  54  and  58,  Part 
I),  with  a  heat  of  formation  of  —47,600  calories.  It  occurs 
also  as  a  product  of  the  distillation  of  wood  and  coal,  and 
hence  in  coal  gas.  It  is  formed,  too,  when  coal  gas  burns 
with  insufficient  air ;  thus  when  the  gas  becomes  ignited  at 
the  base  of  the  Bunsen  burner  the  odor,  very  quickly  noted, 
is  that  of  acetylene.  Another  method  of  making  it  which 
has  attracted  much  attention  of  late  is  by  the  action  of  water 
on  the  carbides  of  such  metals  as  have  a  strong  tendency  to 
seize  on  the  oxygen  of  water,  particularly  calcium  carbide, 
CaCg.  This  substance  is  produced  by  the  reaction  of  lime, 


ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

CaO,  and  charcoal  at  a  very  high  temperature,  which  has 
become  easily  available  since  the  introduction  of  the  elec- 
tric arc  for  heating.  When  calcium  carbide  and  water  are 
brought  in  contact  at  ordinary  temperature,  reaction  takes 
place  as  expressed  in  the  equation 

CaC2  +  H20  =  CaO  +  C2H2. 

The  carbide  has  become  a  commercial  article,  and  compara- 
tively cheap,  and  it  is  proposed  to  supply  it  as  a  source  for 
illuminating  gas.  It  has  also  been  proposed  to  supply  the 
gas  itself  under  pressure  in  transportable  tanks. 
281  Acetylene  is  a  gas  without  color,  but  of  marked  and 
peculiar  odor.  It  is  soluble  in  its  own  volume  of  water. 
Its  specific  gravity  is  13.1  (Moissan).  It  liquefies  under  a 
pressure  of  forty-eight  atmospheres  at  0°.  It  is  poisonous  if 
inhaled  in  considerable  quantity.  Accompanying  its  endo- 
thermic  character  is  its  high  chemical  activity.  Brought 
in  contact  with  a  solution  of  silver  salt,  it  yields  a  white 
precipitate,  and  with  cuprous  salt  a  red  precipitate — a  good 
qualitative  test.  These  substances  have  the  composition 
Ag2C2  and  Cu2C2  respectively,  yield  acetylene  by  treat- 
ment with  acid,  and  when  dry,  are,  very  explosive.  Acety- 
lene, when  pure  and  burned  freely  in  the  air,  shows  a  lumi- 
nous but  smoky  flame ;  but  when  mixed  with  air  in  a  suit- 
able burner,  it  yields  a  very  brilliant  white  light.  The 
heat  given  out  by  the  combustion  of  carbon  and  hydrogen 
is  of  course  greatly  increased  by  the  decomposition  heat  of 
281/1  acetylene.  Indeed,  the  gas  itself  may  be  explosive  under 
certain  conditions ;  for  whatever  would  cause  its  decompo- 
sition into  carbon  and  hydrogen  would  cause  a  sudden 
liberation  of  energy,  although  the  volume  of  gas  produced 
would  not  exceed  the  original  volume.  Under  atmospheric 
pressure  it  does  not  readily  explode,  and  only  by  detonation ; 
but  under  twice  the  atmospheric  pressure  it  may  be  vio- 
lently exploded.  In  England  it  is  reckoned  as  subject  to 
the  law  concerning  explosives,  if  under  a  pressure  of  more 


DESCRIPTION   OF  ELEMENTS  AND  COMPOUNDS    H5 

than  1.05  atmospheres  (i.  e.,  atmospheric  pressure  plus  about 
20  inches  of  water  column) ;  similarly  in  Germany,  if  under 
a  pressure  of  more  than  1.1  atmospheres ;  and  in  France,  if 
under  more  than  1.5  atmospheres.* 

Another  peculiar  feature  of  its  chemical  activity  is  its  281/2 
property  of  combining  with  itself,  which  is  provoked  simply 
by  heating,  and  results  in  the  formation  of  two  volumes  of 
benzene,  C6H6,  from  six  volumes  of  acetylene.  This  is  called 
polymerization  (see  Nos.  85/t,  86,  and  179,  Part  I).  Acet- 
ylene combines  also  with  hydrogen,  forming  ethylene, 
C2H4,  and  ethane,  C2H6.  There  are  only  a  few  homologues 
of  acetylene  known.  Their  general  formula  is  CnH(2n_2). 

One  other  series  should  be  mentioned,  although  it  does  282 
not  by  any  means  exhaust  the  list.  This  is  the  series  of 
which  the  first  member  is  benzene,  C6H6,  and  the  second 
toluene,  C7H8.  Their  general  formula  is  CnH(2,t_6).  They 
are  derived  from  coal  tar,  and  have  a  large  industrial 
importance.  Benzene  is  a  clear,  oil-like  liquid,  of  boiling 
point  80.5°. 

The  hydrocarbons,  therefore,  are  extremely  numerous  283 
and  in  themselves  highly  interesting  substances.  But  more 
than  this,  they  are  the  parent  substances,  so  to  speak,  from 
which  are  derived,  by  definition  at  least,  the  almost  innu- 
merable substances  called  organic  ;  so  called  because  it  was 
formerly  thought  that  their  production  was  dependent  on 
vital  energy.  This  conception  having  changed,  they  are 
now  more  fitly  designated  as  the  hydrocarbons  and  their 
derivatives,  and  they  constitute  the  subject-matter  of  "  Or- 
ganic Chemistry."  This  branch  is  so  extensive  that  its 
literature  is  more  voluminous  than  that  of  all  the  rest  of 
chemistry  put  together. 

5e.  Flame 
See  Nos.  284-292,  Part  II. 

*  Chemical  News,  October  8,  1897. 


116        ELEMENTARY   PRINCIPLES  OF  CHEMISTRY 


293 


294 


5f.  Petroleum 

Petroleum  is  a  liquid  mineral  which  issues  from  the  earth,  or  is 
brought  to  the  surface  by  boring,  in  many  parts  of  the  world.  The 
most  important  sources  are  in  Pennsylvania,  New  York,  Ohio,  West 
Virginia,  and  some  other  districts  in  this  country ;  in  Ontario.  Canada ; 
in  Russia,  on  the  Caspian;  in  Burmah,  India,  and  Japan.  Closely  re- 
lated to  petroleum  is  the  natural  gas  which  likewise  issues  from  the 
earth.  "Burning  springs,  as  they  have  been  termed,  have  been 
known  from  the  earliest  historical  times.  Those  of  Baku,  on  the 
Caspian,  are  supposed  to  have  been  burning  as  early  as  the  sixth  cen- 
tury B.  c.,  and  to  have  been  a  sacred  shrine  of  the  Persian  fire- wor- 
shipers. The  Chinese  have  employed  natural  gas  for  centuries  in 
their  salt  mines  as  a  source  of  light.  In  the  United  States  it  was  em- 
ployed in  1821  at  Fredonia,  New  York,  for  illuminating  purposes;  and 
for  fifty  years  past  it  has  served  as  the  fuel  for  the  evaporation  of  brine 
at  the  salt-wells  of  the  Kanawha  Valley,  West  Virginia."  (Sadtler.) 
Natural  gas  to  the  extent  of  about  ninety  per  cent  is  made  up  of 
methane  and  a  small  quantity  of  one  or  two  of  its  homologues. 

Crude  petroleum  varies  somewhat  in  character.  That  of  Pennsyl- 
vania is  generally  dark,  greenish  black  in  color,  and  red  by  transmitted 
light.  It  is  lighter  than  water,  and  is  essentially  a  mixture  of  paraffin 
hydrocarbons,  some  of  the  gaseous  members  and  some  of  the  solid  being 
dissolved  in  the  liquid.  Its  refining  consists  of  distillation  and  treat- 
ment with  sulphuric  acid,  and  sometimes  dilute  alkali,  to  remove  those 
substances  which  are  objectionable  by  reason  of  their  odor,  and  which 
frequently  contain  sulphur.  The  products  of  petroleum  come  into 
commerce  under  various  names,  the  following  among  them : 


PARAFFINS. 

Name. 

Boiling 
point. 

Uses. 

Below  Co 

Cymojrene 

0° 

Manufacture  of  ice. 

C^  * 

Rhigolene 

18° 

Anjesthetic  in  medicine. 

C5-6       
Ce_  7 

Petroleum  ether. 
Gasolene 

40°-70° 
70°-90° 

As  a  solvent  and  in  gas-making. 
As  a  solvent  and  in  gas-making. 

C7_g    

Naphtha,  or  li- 

crroine 

80°-120° 

As  a  solvent  and  as  fuel. 

Cfi_0 

Benzine 

120°-150° 

As  a  solvent. 

Cm  i« 

Kerosene     

150°-300° 

Illuminating  oil. 

295  Other  liquid  portions  find  use  as  lubricating  oils ;  and  the  solids  of 
lowest  melting  point,  40°-50°,  n  =  21-23,  appear  as  vaseline ;  and  of 
melting  point  from  51°-57°,  n  =  22-28,  as  the  white  paraffin  which  is 


DESCRIPTION   OF   ELEMENTS  AND   COMPOUNDS    117 

familiar  in  the  laboratory.  The  latter  is  used  largely  in  candle-making, 
in  finishing  calicoes  and  similar  goods  to  give  a  luster  to  the  surface, 
in  waterproofing  paper,  in  making  Swedish  matches,  and  in  extracting 
perfumes  from  flowers.  (Mostly  according  to  Sadtler.) 

The  presence  in  kerosene  of  the  easily  volatile  and  inflammable  296 
members  of  the  series  must  make  its  use  as  an  illuminating  oil  more  or 
less  dangerous.  The  public  is  protected  in  many  countries  by  legisla' 
tion  making  it  unlawful  to  Sell  for  such  purpose  an  oil  which,  below  a 
specified  temperature,  gives  off  vapor  enough  to  be  ignited.  This  tem- 
perature is  called  the  flashing  point,  and  it  is  determined  for  a  given 
sample  by  heating  in  a  suitable  vessel  until  by  trial  the  vapor  above 
the  liquid  inflames  with  a  match,  when  the  temperature  is  noted.  In 
many  of  the  states  the  flashing  point  is  fixed  at  44°  (111°  F.);  in  some 
as  high  as  65|°  (150°  F.). 

There  has  been  much  speculation  as  to  how  petroleum  has  been  297 
produced  in  nature.  Mendeleeff  has  suggested  that  it  is  by  the  action 
of  water  penetrating  from  the  surface  and  coming  in  contact  with 
metallic  carbides  at  great  depth.  This  is  rendered  probable  by  the  fact 
that  carbides  are  made  artificially  at  very  high  temperature,  and  that 
some  of  them  react  with  water,  yielding  hydrocarbons. 


5g.   Coal 

When  wood  and  similar  plant  substances  decay  without  free  access  298 
of  air,  chemical  changes  take  place  by  which  methane  and  carbon 
dioxide  are  separated,  and  at  the  same  time  the  residue  contains  a 
larger  proportion  of  carbon.  This  is  somewhat  similar  in  effect  to  the 
change  produced  more  rapidly  in  the  charring  by  heat.  The  process 
of  decay  is  seen  going  on  in  the  accumulations  of  vegetable  matter  in 
swamps  and  at  the  bottom  of  shallow  pools  as  already  suggested  in 
another  connection ;  also  in  the  vegetable  mold  of  leaves  close  to  the 
surface  of  the  ground  in  the  woods.  In  some  places  this  material  has 
accumulated  so  that  it  can  be  removed  like  a  thick  turf,  and  it  is  used 
as  a  poor  kind  of  fuel,  known  as  peat  or  turf.  By  some  such  process  299 
as  this,  lasting  through  ages  and  modified  by  heat  and  pressure,  it  is 
supposed  that  the  accumulated  vegetation  of  a  period  before  the  appear- 
ance of  man  on  the  earth,  when  plant  growth  was  more  abundant  than 
now,  has  been  converted  into  beds  of  coal.  These  have  become  very 
valuable  as  a  store  of  fuel,  and  hence  of  energy,  and  very  essential 
to  the  life  and  activities  of  the  present.  Lignite  is  a  variety  of  coal 
which  still  shows  traces  of  the  woody  structure,  and  hence  is  of  the 
more  recent  formation.  Bituminous  or  soft  coal  has  lost  the  plant 


118        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

structure,  but  still  contains  much  hydrogen,  and  hence  yields  volatile 
matter  by  heating,  and  burns  with  a  flame.  From  such  coal  illu- 
minating gas  is  made  by  distillation.  Anthracite  is  harder,  denser, 
shows  more  luster,  and  burns  with  little  or  no  flame.  Its  content  of 
carbon  is  higher,  and  it  must  be  the  oldest  in  order  of  formation. 
Some  varieties  seem  to  have  passed  almost  into  graphite.  The  follow- 

300  ing  table  of  percentage  composition  shows  the  gradual  accumulation  of 
carbon  through  these  periods  of  transformation : 

C  H 

Wood *.....  50  6.0 

Peat 60  5.9 

Lignite 70  5.0 

Bituminous 88  5.6 

Anthracite. 94  3.4 

Charcoal 96  0.6    Made  at  white  heat  (1,500°). 

Charcoal 75  4.4    Made  at  340°. 

5h.   Coal  Gas 

301  The  important  industry  of  making  illuminating  gas  from  coal 
originated  with  a  Scotchman,  William  Murdoch.    In  1798  a  factory 
was  lighted  by  his  process.     Gas  was  used  for  street  lighting  in  Lon- 
don in  1812,  and  in  Paris  about  1815.     The  process  of  manufacture  in 
brief  consists  of  heating  bituminous  coal  to  a  high  temperature  in 
retorts  of  iron  or  fire  clay.     The  gas  is  cooled  and   passed  through 
water,  by  which  tar  is  deposited  and  the  ammonia  which  comes  from 
the  nitrogen  of  the  coal  is  removed.     This  constitutes  the  chief  com- 
mercial source  of  ammonia.    From  the  remaining  gas  such  impurities  as 
hydrogen  sulphide,  carbon  disulphide,  and  carbon  dioxide  are  removed 
by  the  agency  of  slaked  lime  or  iron  hydroxide.     The  general  composi- 
tion of  purified  gas  is  shown  in  the  following  percentages  (Sadtler) : 

302  Hydrogen 37.97 

Methane 39.37 

Carbon  monoxide 3.97 

Olefins  and  other  heavy  hydrocarbons 4.29 

Nitrogen -  9 . 99 

Oxygen 0. 61 

Carbon  dioxide 0.41 

The  solid  residue  of  the  retorts  is  coke.  From  the  coal  tar,  sub- 
stances of  great  variety  are  obtained — such  as  benzene  and  its  homo- 
Jogues,  carbolic  acid,  naphthalene,  pitch,  and  many  others, 


DANIEL  RUTHERFORD 

B.  Edinburgh,  1749.     D.  1819. 

(See  Nos.  306,  388.) 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   H9 

5i.  Destructive  Distillation  of  Wood 

Closely  analogous  to  the  distillation  of  coal  is  that  of  wood,  which  303 
has  come  to  be  a  considerable  industry.  The  primitive  and  crude 
method  of  charring  wood  in  pits  and  mounds  was  for  the  charcoal 
only.  Improved  methods  have  produced  valuable  material  from  the 
gaseous  and  liquid  portions  formerly  wasted.  Heated  below  150°, 
wood  loses  water  only — from  20  to  50  per  cent,  according  to  the  variety. 
From  150°  to  280°  the  dry  wood  loses  about  64  per  cent  of  its  weight  in 
volatile  products ;  from  280°  to  350°  it  loses  about  6.5  per  cent ;  from 
350°  to  430°,  about  10  per  cent ;  from  430°  to  1,500°,  only  about  2  per 
cent ;  so  that  the  yield  of  charcoal  varies  from  18  to  20  per  cent. 
From  the  distillate  between  150°  and  280°  are  obtained  pyroligneous  304 
acid  or  wood  vinegar  (a  crude  acetic  acid) ;  wood  naphtha,  or  wood 
alcohol,  which  is  impure  methyl  alcohol,  CH40,  a  substance  homologous 
with  common  alcohol,  C3H60,  and  very  similar  to  it;  and  wood  creo- 
sote. The  distillate  between  280°  and  350°  is  mostly  gaseous  hydro- 
carbons, and  that  from  350°  to  430°  liquid  and  solid  hydrocarbons. 
The  yield  of  charcoal  is  greater  from  slow  heating  than  from  quick; 
it  is  sometimes  more  than  30  per  cent  of  the  dried  wood.  Besides  the 
charcoal, the  chief  commercial  products  obtained  after  various  purifica-  305 
tions  are  acetic  acid  and  acetates — e.  g.,  of  iron,  calcium,  and  sodium, 
which  have  uses  especially  in  the  dyeing  industries;  methyl  alcohol,  or 
wood  spirit,  used  as  a  solvent  in  making  varnishes,  etc.,  and  in  making 
aniline  dyestuffs ;  acetone,  used  especially  as  a  solvent ;  and  creosote, 
used  as  an  antiseptic  or  preservative.  (Sadtler.) 


6.  NITROGEN 

N. -13.93 

History. — Rutherford  and  Priestley  in  1772  had  under  investigation  306 
what  was  later  recognized  as  nitrogen,  but  Lavoisier  was  the  first  to 
show  the  elementary  nature  of  the  substance  and  its  true  relation  to  the 
atmosphere.  He  also  named  it  azote,  and  it  still  goes  by  this  name  in 
French  literature.  The  name  nitrogen  comes  from  nitrum  or  niter,  the 
common  name  for  potassium  nitrate. 

Natural  occurrence, — Nitrogen  exists  uncombined  in  the  307 
atmosphere,  of  which  it  forms  about  four  fifths  in  volume. 
It  is  a  constituent  of  nitric  acid  and  its  salts,  also  of  am- 
monia and  its  salts,  and  of  many  organic  substances.     In- 


IT 

120        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

deed,  it  plays  an  important  part  in  the  life  of  both  plant  and 
animal,  and  is  an  essential  element  in  their  food. 

308  Preparation. — The  common  source   of  nitrogen  is  air, 
from  which  the  oxygen  may  be  removed  by  some  strongly 
combustible  substance  like  phosphorus,  or  even  by  red-hot 
copper ;  and  copper  shavings  moistened  with  ammonium 
hydroxide  absorb  oxygen  at  ordinary  temperature.     Other 
methods  of  preparing  are  interesting  simply  as  chemical 
reactions.     Thus,  by  heating  a  concentrated  solution  of 
ammonium  nitrite,  the  reaction  expressed  by  the  following 
equation  takes  place : 

(1)  NH4N02  =  2N  +  2H20. 

Also,  by  removing  the   hydrogen  from   ammonia,  nitro- 
gen is  liberated : 

(2)  ]STH3  +  301  =  N  +  3HC1. 

309  Properties. — Nitrogen  is  a  gas  without -colo*r  or  odor,  of 
specific  gravity  a  little  less  than  that  of  air.     One  hundred 
volumes  of  water  dissolve  only  one  aijd  a  half  of  the  gas  at 

J  ordinary  temperature.  It  is,  condensable  to  a  liquid  which 
is  lighter  than  water  and  which  boils  at  —  194°  and  solidi- 
fies at  -214°. 

310  It  has  no  action  on  litmus,  is  neither  combustible  nor  a 
supporter  of  combustion,  is  not  poisonous,  but  is  incapable 
of  sustaining  life.     Its  chemical  inertia  is  its  most  strik- 
ing characteristic,  as  under  ordinary  circumstances  it  reacts 
with  nothing ;  yet  its  compounds  are  numerous  and  varied, 
and  among  the  most  interesting.     At  red  heat  it  combines 
directly  with  boron,  magnesium,  silicon,  titanium,  and  vana- 
dium, forming  stable  compounds.     Under  the  influence  of 
electric  discharge  nitrogen  combines  with  oxygen,  also  with 
hydrogen,  so  that  nitric  acid  and  ammonia  are  formed  in 
small  quantities  during  thunderstorms  and  are  washed  down 
in  the  rain.     In  the  presence  of  alkali  carbonate  it  combines 
with  red-hot  carbon,  forming  cyanogen,  C2N2.     Under  silent 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   121 

electric  discharge  it  combines  with  some  organic  substances 
like  cellulose  (filter  paper),  glucose  (a  kind  of  sugar),  and 
benzene. 

In  combination  with  oxygen  it  forms  a  series  of  five   311 
oxides,  a  most  remarkable  instance  of  multiple  proportions. 
The  names  and  formulas  of  the  oxides  are  as  follows  : 

(1)  N20,  nitrogen  monoxide,  or  nitrous  oxide. 

(2)  NO,  nitrogen  dioxide,  or  nitric  oxide. 

(3)  N203,  nitrogen  trioxide,  or  nitrous  anhydride. 

(4)  N204,  nitrogen  tetr oxide. 

(5)  N205,  nitrogen  pentoxide,  or  nitric  anhydride. 

Of  these,  the  first,  third,  and  fifth  are  acid-forming  ox- 
\  ides ;  the  second  and  fourth  are  neutral  oxidesk 

6a.  Nitrogen  Monoxide,  N20 

This  gas  was  discovered  by  Priestley  in  1776.  It  is  not  312 
found  as  a  natural  substance.  It  is  formed  to  some  extent 
by  the  action  of  nitric  acid  on  metals,  particularly  at  a  low 
temperature  and  when  the  acid  is  dilute ;  but  it  is  best  made 
by  heating  the  dry  salt,  ammonium  nitrate,  when  the  reac- 
tion expressed  by  the  following  equation  takes  place : 

NH4N03  =  X20  +  2H20. 

This  reaction  is  exothermic,  liberating  31,000  calories. 

Mtrogen  monoxide  is  a  gas  without  color,  but  with  a  313 
slight  odor  and  taste.     One  hundred  volumes  of  water  at 
ordinary  temperature  dissolve  about   seventy  volumes  of 
the  gas.     Its  specific  gravity  is  about  one  and  a  half  times 
that  of  air — i.  e.,  21.99  (H  =  1).     It  is  condensable  to  a 
liquid,  which  boils  at  about   —  90°  and  freezes  at  about  . 
—  100°.     The  gas  has  no  action  on  litmus,  although  when  314 
combined  with  water  it  forms  hyponitrous  acid,  which,  how- 
ever, is  very  unstable.    The  freezing-point  method  (see  Nos. 
Ill  and  155)  indicates  the  formula 

H2O.X20,  or  H2N202. 


122        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

The  sodium,  potassium,  and  silver  liyponitrites  are  known, 
and  have  the  formulas,  respectively,  Na2N202,  K2IST202,  and 
Ag2X202.  The  gas  is  composed  of  two  volumes  of  nitrogen 
and  one  of  oxygen  in  .two  volumes  of  the  oxide.  Its  heat  of 
formation  is  negative,  —18,000  calories.  This  accounts  for 
the  fact  that  the  gas  supports  combustion  if  the  combusti- 
ble is  already  ignited  and  if  it  produces  enough  heat  to  de- 
compose the  nitrous  oxide.  Thus  a  candle,  burning  bright- 
ly, and  sulphur  thoroughly  ignited,  and  phosphorus  continue 
to  burn  in  the  gas,  but  they  may  be  extinguished  if  not 
already  burning  vigorously.  It  is  also  notable  that  if  they 
burn,  they  burn  more  brightly  than  in  air.  The  cause  of 
this  may  be  the  fact  that  nitrous  oxide,  when  decomposed, 
yields  a  mixture  which  is  one  third  oxygen,  whereas  the  air 
is  only  one  fifth  oxygen.  A  mixture  of  nitrous  oxide  and 
hydrogen  explodes  like  hydrogen  and  air,  forming  water 
and  nitrogen  : 

X20  +  2H  =  2X  +  H20. 

315  While  nitrous  oxide  thus  readily  gives  up  its  oxygen,  it 
does  not  easily  combine  with  oxygen  as  does  nitric  oxide. 
It  is  interesting  to  note  that  if  nitrous  oxide  combined 
directly  with  oxygen  to  form  nitric  oxide,  thus, 

N0       0  = 


the  reaction  would  involve  the  formation  of  four  volumes 
of  the  product  from  (2  -\-  1)  volumes  of  the  factors,  that  is, 
expansion  of  volume  which  would  be  extraordinary.  Fur- 
thermore, the  reaction  would  be  accompanied  by  the  absorp- 
tion of  about  25,000  calories  of  heat  energy.  On  the  other 
hand,  the  oxidation  of  nitric  oxide  liberates  heat,  thus  : 


+  20  =  X204  +  about  40,000  calories. 

316  Nitrous  oxide  when  inhaled  pure  produces  insensibility, 
which  ultimately  ends  in  death  byr  suffocation,  but  which 
passes  off  if  the  supply  of  oxygen  be  quickly  restored  to  the 
lungs.  It  is  used  extensively  as  an  anaesthetic  when  insen- 


DESCRIPTION  OF  ELEMENTS  AND   COMPOUNDS   123. 

sibility  for  a  short  period  is  desired.  If  inhaled  with  air 
it  produces  a  kind  of  intoxication,  which  led  to  the  name 
"laughing-gas." 

6b.  Nitrogen  Dioxide,  NO 

Nitrogen  dioxide,  or  nitric  oxide,  is  not  found  as  a  natu-  31  7 
ral  substance.  It  is  prepared  by  removing  oxygen  from  a 
higher  oxide,  the  pentoxide,  which  is  contained  in  nitric 
acid.  This  is  most  conveniently  done  by  the  agency  of 
metallic  copper  or  ferrous  sulphate.  When  copper  is  used, 
the  acid  should  be  somewhat  dilute  (sp.  gr.  1.18)  ;  small 
quantities  of  other  nitrogen  oxides  may  be  formed  at  the 
same  time. 

The  following  equations  may  serve  to  explain  the  com- 
plex nature  of  the  reaction  : 

(1)  2HNOS  =  H2N206  =  N205-H20. 

(2)  N808  =  2NO  +  30. 

(3)  30  +  3Cu  =  3CuO. 

(4)  3CuO  +  6HN03  =  3Cu(N08)8  +  3H20. 

The  whole  may  be  expressed  in  one  equation,  thus  : 
3Cu  +  8HN03  =  3Cu(N03)2  +  4H20 


With  ferrous  sulphate,  the  reaction  is  similar  so  far  as 
the  nitrogenous  substances  are  concerned,  but  by  the  oxy- 
gen which  the  nitric  acid  loses,  the  iron  oxide  of  the  salt  is 
changed  from  ferrous  oxide,  FeO,  to  ferric  oxide,  Fe203,  and 
consequently  the  ferrous  salt  becomes  ferric  salt.  (See 
Nos.  47/4  and  48,  Part  II.) 

Nitric  oxide  is  a  colorless  gas,  and  when  pure  has  no  318 
action  on  litmus.  Its  specific  gravity  is  14.95  (H  =  1). 
One  hundred  volumes  of  water  dissolve  about  five  of  the 
gas  at  ordinary  temperature,  but  it  does  not  combine  with 
water  and  has  no  acid-forming  property.  It  is  condensable 
to  a  colorless  liquid  which  boils  at  —154°  and  solidifies  at 
—  167°.  Like  nitrous  oxide,  it  is  endothermic  with  a  for- 


124        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

mation  heat  of  —  21,600  calories,  but  it  is  apparently  more 
stable  than  the  former,  and  burning  sulphur  and  wood  are 
extinguished  by  it.  Phosphorus  and  some  metals,  strongly 
heated,  take  oxygen  from  it.  The  vapor  of  carbon  disul- 
phide,  which  also  is  highly  endothermic,  burns  in  it  with 
intense  brilliancy.  On  the  other  hand,  it  combines  directly 
with  oxygen  on  contact  at  ordinary  temperature,  forming 
the  tetroxide.  It  dissolves  in  a  solution  of  ferrous  sulphate, 
combining  with  the  latter,  but  the  product  is  very  unstable. 
It  combines  with  chlorine  at  red  heat  (Ramsay).  The  gas 
itself  may  be  exploded  by  the  shock  of  another  explosion, 
such  as  that  of  the  fulminate  in  a  common  percussion  cap 
(Berthelot). 

6c.  Nitrogen  Trioxide^  N20$ 

819  This  substance  is  very  unstable,  and  probably  does  not 
exist  in  gaseous  condition,  but,  when  vaporized,  becomes  a 
mixture  of  nitric  oxide  and  the  tetroxide  ;  thus  : 


But  when  the  mixture  of  these  gases,  or  of  nitric  oxide 
and  oxygen  (2NO  -f  0),  is  cooled,  a  dark-blue  liquid  is 
produced  which  is  supposed  to  be  the  trioxide.  This,  even 
below  0°,  gives  off  the  brown  gas  which  is  a  mixture  of  the 
two  oxides.  If  this  mixture  is  passed  into  a  solution  of 
basic  hydroxide,  a  salt  is  formed  which  is  evidently  the  salt 
of  the  trioxide  ;  thus  : 

NO  +  N02  +  Na2O.H20  =  H20  +  Na2O.N203  or  SNaNOg. 

320  This  is  called  nitrite,  and  corresponds  to  the  acid,  HX02. 
But  when  sulphuric  acid  is  added  to  the  solution  of  nitrite 
in  order  to  liberate  this  nitrous  acid,  the  latter  immediately 
breaks  up  into  water  and  the  dioxide  and  tetroxide.  When 
the  liquid  trioxide  is  mixed  with  ice  water  it  is  supposed 
that  some  nitrous  acid  is  produced  ;  thus  : 

N203  +  H20  = 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    125 

But  with  a  slight  rise  of  temperature  this  becomes  nitric 
acid  and  nitric  oxide ;  thus  : 

3N203  +  H20  =  4X0  +  N205-H20,  or  2H]ST03 ; 

And  so,  again,  a  higher  and  a  lower  oxide  are  produced. 

Nitrous  acid  in  dilute  solution,  or  its  anhydride  (N203), 
has  the  curious  property  of  acting  both  as  an  oxidizing  and 
as  a  reducing  agent ;  in  oxidizing,  it  splits  into  2NO  and  0 ; 
in  reducing,  it  becomes  the  pentoxide,  N205.  Thus  it  oxi- 
dizes the  hydrogen  of  hydriodic  acid,  HI,  liberating  the 
iodine ;  but  it  reduces  permanganate,  destroying  its  color. 

The  nitrites  are  comparatively  stable.     They  are  found  321 
sometimes  in  minute  quantity  in  rain  water  and  snow,  com- 
ing from  the  atmosphere,  and  they  occur  in  some  plant 
juices. 

6d.  Nitrogen  Tetr oxide,  NZ0± 

This  substance  is  formed  by  direct  reaction  between  ni-  322 
trie  oxide  and  oxygen  or  air  (compare  Exps.  47/i  and  47/8) 
at  ordinary  temperature  with  evolution  of  heat,  39,200  cal- 
ories.    It  is  also  formed  when  some  nitrates  are  heated. 
Lead  nitrate  is  commonly  used.     (Compare  Exps.  16/j  and 

16AO 

Pb(N03)2  (dry  and  heated)  =  PbO  +  0  +  N204  or  2N02. 

This  oxide  of  nitrogen  at  sufficiently  low  temperature  323 
is  a  colorless  solid,  which  melts  at  — 10°  to  a  pale-yellow 
liquid.  This  becomes  darker  as  the  temperature  rises  until 
at  22°  it  boils  and  the  vapor  is  reddish  brown.  The  color 
continues  to  grow  deeper  until  the  temperature  passes  140°, 
when  it  begins  to  fade,  and  at  600°  or  higher  the  gas  is 
colorless.  The  specific  gravity  of  the  liquid  is  1.45  (water 
=  1) ;  that  of  the  vapor  just  above  the  boiling  point  (H  = 
1)  is  such  as  to  indicate  (Gay-Lussac's  law ;  see  No.  94)  the 
formula  N204,  but  at  140°  it  indicates  N02,  and  at  600°  or 
more  the  gas  is  simply  a  colorless  mixture  of  nitric  oxide  and 


126        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

oxygen.  When  this  mixture  cools,  the  gaseous  substance 
N02  is  first  formed,  then  the  gas,  N204,  then  the  liquid,  and 
finally  the  colorless  solid.  (Compare  with  sulphur.  See  No. 
93.)  Therefore  the  solid,  the  liquid,  and  the  colorless  gas, 
N204,  are  to  be  considered  as  polymeric  (see  No.  179)  with  the 
dark-colored  gas,  N02.  It  is  convenient  to  designate  the  sub- 
stance X02  as  the  peroxide  and  N204  as  the  tetr oxide.  When 
the  peroxide  combines  with  itself  heat  is  liberated ;  thus  : 

N02  +  N02  =  N204  +  12,900  calories. 

324  The  gas  has  a  peculiar  odor,  and  is  poisonous.     It  is 
an  energetic  oxidizer  and  corrosive.     Phosphorus  may  be 
made  to  burn  in  it,  and  it  attacks  many  organic  substances, 
producing  yellow  derivatives.     It  dissolves  in  concentrated 
nitric  acid,  forming  the  so-called  fuming  nitric  acid  of  com- 
merce.    It  forms  with  water  no  acid  of  which  it  may  be 
regarded  as  the  anhydride,  but  with  ice  water  it  gives  both 
nitrous  and  nitric  acids  : 

N204  +  H20  =  HN02  +  HN03. 

At  ordinary  temperature  and  with  excess  of  water  the  re- 
action is 

3N804  +  2H20  =  4HN03  +  2NO. 

6e.  Nitrogen  Pentoxide,  N205 

325  This  substance  is  prepared  by  removing  water  from 
nitric  acid,  N20.5H20,  by  means  of  phosphorus  pentoxide, 
P205,  and  distilling  the  residue  at  low  temperature.     It 
forms  colorless,  transparent  crystals,  which  melt  at  30°  and 
boil  at  about  45°.     The  heat  of  formation  of  the  solid  is 
13,100  calories ;  but  that  of  the  gas,  curiously  enough,  is 
about  zero.     It  is  very  unstable,  breaking  up  even  explo- 
sively into  the  tetroxide  and  oxygen.     It  combines  with 
water  very  energetically,  liberating  heat  and  forming  nitric 
acid. 

N205  +  H20  =  H8N806  =  '2HN08. 


DESCRIPTION  OP  ELEMENTS  AND  COMPOUNDS  127 

61  Nitric  Acid,  HNOS 

This  substance  was  known  to  the  Arabian  alchemists,  326 
the  earliest  account  of  its  preparation  being  that  of  Geber 
in  the  eighth  century.  He  made  it  by  heating  a  mixture 
of  potassium  nitrate,  copper_sulphate,  and  alum.,  Glauber 
(1603-768)  made  it  from  niter  (potassium  nitrate)  and  sul- 
phuric acid,  whence  its  modern  name.  It  has  been  called 
"  aqua  fortis,"  from  its  property  of  attacking  metals.  La- 
voisier in  1776  showed  that  it  contained  oxygen,  and  Cav- 
endish (1784-J85)  showed  its  relation  to-  nitrogen,  oxygen, 
and  water. 

It  occurs  in  nature  free  in  small  quantities,  but  princi-  327 
pally  and  abundantly  in  its  salts,  the  nitrates  of  potassium 
and  sodium. 

Nitric  acid  is  formed  in  small  quantity  from  nitro-  328 
gen,  oxygen,  and  water  vapor  by  electric  discharge,  and  is 
therefore  found  in  the  atmosphere.  It  is  also  formed  as 
nitrate  by  the  oxidation  of  (ammonia  and  of  the  nitrogen  of 
organic  substances  in  the  presence  of  bases.  This  process 
is  called  nitrification,  and  goes  on  in  the  soil.  It  is  de- 
pendent upon  thex  presence  of  minute  living  organisms, 
called  bacteria,  or  at  least  it"  is  greatly  influenced  thereby. 

Nitric  acid  is  formed,  too,  when  hydrogen  is  burned  in 
oxygen  with  a  small  quantity  of  nitrogen  present,  and 
when  ammonia  is  burned  in  oxygen. 

The  chief  artificial  method  of  preparation,  both  on  a  329 
large  and  a  small  scale,  is  by  the  action  of  sulphuric  acid  on 
sodium  or  potassium  nitrate,  and  the  distillation  of  the 
more  volatile  nitric  acid  thus  set  free.     With  excess  of  sul- 
phuric acid,  the  reaction  is  as  expressed  in  the  equation 

NaN03  +  H2S04  =  NaHS04  +  HN03 . 

Nitric   acid  is   an  important  commercial  article,  and  330 
comes  into  the  market  as  a  water  solution  of  specific  grav- 
ity 1.4,  and  containing  only  about  60  per  cent,  or  less,  of 


128        ELEMENTARY   PRINCIPLES  OF  CHEMISTRY 

the  true  acid.     This  is  likely  to  contain  as  impurities  sul- 
phuric acid  and  hydrochloric  acid,  or  chlorine,  and  iron  salt. 

331  When  freed  of  these  and  of  most  of  the  solvent  water, 
it  appears  as  a  colorless  liquid  with  a  specific  gravity  of 
about  1.53,  and  contains  about  99.5  per  cent  of  the  true  acid, 
HN03 .    It  fumes  in  the  air  and  absorbs  water  energetically. 
It  boils  at  86°  and  solidifies  at  about  —50°.     When  boiled, 
and  even  at  ordinary  temperature,  it  decomposes  to  some 
extent  into  the  tetroxide,  oxygen,  and  water  ;  as  a  result  of 
this  the  liquid,  even  when  more  dilute,  becomes  somewhat 
yellow  and  shows  the  brown  fumes.     At  a  higher  tempera- 
ture, 256°,  the   decomposition  is  complete.     The  specific 
gravity  of  the  vapor  slightly  above  the  boiling  point  is  29.7 
(H  =  1),  indicating  the  formula  HX03.     The  substance  is 
very  corrosive,  attacking  many  substances  violently,  and 
showing  a  marked  tendency  to  stain  organic  matter  yellow. 
WThen  the  concentrated  acid  is  diluted  with  water,  heat  is 
liberated,  and  the  boiling  point  of  the  dilute  acid  is  higher 
than  that  of  the  concentrated,  and  higher  than  that  of 
water.     If  the  dilute  acid  is  distilled,  it  is  chiefly  water 
that  passes  over  until  the  boiling  point  reaches  121°  (nor- 
mal pressure),  when  it  remains  constant,  and  the  distillate 
contains   uniformly  about  70  per  cent  of  the  true  acid. 
This  is  supposed  to  be  combined  with  the  water.     On  the 
other  hand,  a  solution  containing  more  than  70  per  cent 
of  acid,  fumes,  losing  acid,  and  when  distilled  the  boiling 
point  rises  until  121°  is  reached,  when  the  same  constant 
distillate  is  obtained.     It  has  already  been  noted  that  when 
dilute  nitric  acid  acts  upon  metals,  reduction  products  are 
obtained,  as  well  as  the  salts. 

332  Nitric  acid  is  consumed  in  large  quantities  in  various 
industries — for  example,  in  the  manufacture  of  sulphuric 
acid,  of  dyestuffs,  of  nitroglycerine,  of  guncotton,  of  the 
nitrates  of  silver,  lead,  and  iron ;  in  the  etching  of  stone, 
steel,  and  copper ;  in  the  refining  of  gold  and  silver,  etc. 
It  is  also  an  important  laboratory  reagent. 


DESCRIPTION   OF  ELEMENTS  AND   COMPOUNDS    129 

6g.  The  Nitrates 

Mtric  acid,  as  shown  by  its  formula,  contains  one  com-  333 
bining  weight  of  hydrogen,  replaceable  by  its  equivalent  of 
metal.  Such  an  acid  is  called  monobasic,  It  forms  a  series 
of  well-defined  salts,  which  as  a  rule  are  soluble  jn  water. 
The  chief  natural  nitrates  are  those  of  potassium  and 
sodium,  which  are  also  important  commercial  articles.  The 
most  abundant  is  sodium  nitrate,  which  is  found  in  vast 
beds  in  portions  of  Chili  and  Peru.  It  goes  commercially 
under  the  name  of  Chili  saltpeter.  This  has  been  produced 
probably  by  the  nitrification  of  organic  matter  deposited 
in  what  was  once  the  bed  of  the  sea.  Before  these  beds 
were  worked,  potassium  nitrate,  for  which  there  is  a  large 
demand,  came  mainly  from  somewhat  similar  deposits  in 
India,  particularly  in  Bengal,  where  the  process  of  nitri- 
fication was  artificially  cultivated,  Now  it  is  made  largely 
by  reaction — double  exchange — between  sodium  nitrate  and 
potassium  chloride.  It  is  used  in  making  gunpowder  and 
other  explosives,  and  matches ;  in  curing  meat,  in  refining 
metals,  and  in  medicine.  For  some  of  these  purposes  the 
sodium  nitrate  is  unsuited  by  reason  of  its  hygroscopic 
character,  but  it  is  used  as  a  fertilizer,  and  in  the  manu- 
facture of  nitric  acid  and  potassium  nitrate. 

6h.  Ammonia,  NH3 

,  The  salts  of  this  substance  were  known  to  the  early  334 
alchemists,  especially  the  carbonate  and  the  chloride. 
This  was  called  sal  ammoniac.  Priestley  in  1774  separated 
the  gas,  ammonia.  This  is  formed  in  the  decay  of  plant 
and  animal  substances  containing  nitrogen,  and  also  when 
such  substances  are  subjected  to  dry  distillation.  It  oc- 
curs naturally  in  small  quantities  in  the  atmosphere  and 
water,  and,  as  a  constituent  of  its  salts,  in  the  soil,  and  in 
plant  juices  and  animal  fluids.  But,  as  a  commercial  prod- 


130        ELEMENTARY   PRINCIPLES  OF  CHEMISTRY 

uct,  it  is  artificial,  its  chief  source  being  the  gas  works. 
The  coal  which  is  distilled  contains  some  nitrogen,  about 
2  per  cent,  and  this  appears  as  ammonia,  a  secondary 
product,  in  the  manufacture  of  coal  gas.  It  comes  into 
commerce  as  a  water  solution  which  is  known  as  liquor  or 
aqua  ammonia,  and  contains  from  10  to  30  per  cent  of 
ammonia  gas.  A  number  of  its  salts  are  also  commercial 
articles.  From  its  water  solution  it  may  be  obtained  by 
heating  simply^  and  from  its  salts  by  heating  with  lime, 
or  any  non-volatile  base. 

335  The  gas,  ammonia,  is  without  color,  but  has  an  extremely 
pungent  odor.     Its  specific  gravity  is  8.48  (H  =  1),  and  it 
condenses  to  a  liquid  which  boils  at  about  —40°  and  solidi- 
fies at  about  — 80°.     It  can  be  inhaled  only  when  very 
much  diluted  with  air,  otherwise  it  is  corrosively  poisonous. 
Although  its  heat  of  formation  is  12,000  calories,  it  is  not 
formed,  save  in  very  minute  quantity,  by  direct  combina- 
tion of  nitrogen  and  hydrogen.     When  formed,  it  is  rela- 
tively very  stable.    By  the  passage  of  electric  sparks  and  by 
a  temperature  above  500°,  it  is  slowly  decomposed  into 
three  volumes  of  hydrogen  and  one  of  nitrogen  from  two 
of  ammonia.      It    reacts    at    ordinary   temperature   with 
chlorine  in  the  presence  of  water,  forming  hydrochloric 
acid  and  pure  nitrogen,  which  is  in  volume  equal  to  one 
half  that  of  the  ammonia  decomposed.     It  burns  in  oxygen 
with  a  peculiar,  pale-yellow  flame,  forming  water,  nitrogen, 
and  some  traces  of  nitrogen  oxides.     In  air  it  burns  only 
with  difficulty,  the  resulting  temperature  being  insufficient 
to  maintain  the  combustion  when  it  is  started.     It  reacts 
with  many  other  substances,  with  acids,  and  with  many  salts. 

336  In   water  it    dissolves    in    enormous    proportion,   one 
volume  of  water  dissolving  about  700  volumes  of  the  gas 
at  ordinary  temperature ;  much  heat  is  thereby  liberated, 
8,400  calories  for  17  grams  of  ammonia.     The  gas,  how- 
ever, is  readily  and  completely  expelled  from  the  solution 
by  a  rise  of  temperature,  and  of  course  an  equal  quantity 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    131 

of  heat  is  absorbed  in  the  process.  The  solution  is  lighter 
than  water,  is  alkaline  in  reaction,  caustic,  neutralizes 
acids  and  forms  salts,  and  reacts  in  general  like  the  alkali 
hydroxides  —  e.  g.,  sodium  hydroxide,  NaOH.  From  this 
fact  it  is  supposed  that  ammonia  combines  with  water  addi- 
tively  —  that  is,  in  such  a  manner  that  the  product  contains 
all  the  constituents  of  the  factors  ;  and,  after  analogy  with 
the  alkali  hydroxides,  the  product  is  written  NH4OH,  and 
named  ammonium  hydroxide,  although  there  is  little  direct 
evidence  of  its  existence.  The  name  implies  a  substance, 
ammonium,  NH4,  but  no  such  substance  has  ever  been 
separated.  Ammonia  combines  with  acids  —  e.  g.,  hydro- 
chloric, additively  ;  thus  : 


The    salt    is   written   NH4C1,   and  named  ammonium  337 
chloride,  as  if  it  were  formed  by  displacing  the  hydrogen 
of  the  acid  by  the  substance  ammonium,  as  sodium  forms 
sodium  chloride,  NaCl.     When,  however,  the  salt  is  formed 
from  the  hydroxide  and  the  acid,  the  equation  stands, 

NH4OH  +  HOI  =  NH4C1  +  H20. 

Ammonia,  or  its  solution,  is  used  extensively  —  e.  g.,  in  338 
pharmacy,  in  calico  printing,  in  manufacturing  dyestuffs, 
soda  (i.  e.,  sodium  carbonate),  and  ice.  Ammonium  sulphate 
is  used  in  making  alum  and  as  a  fertilizer,  particularly  for 
sugar-beet  culture.  The  chloride,  also  known  as  sal  am- 
moniac, is  used  in  pharmacy,  in  soldering,  in  galvanizing 
iron,  and  in  dyeing.  The  carbonate  also  is  used  in  dyeing. 

6i.   Other  Compounds  of  Nitrogen 

Besides  the  reactions  already  described,  ammonia  takes  part  in   339 
changes  of  a  different  type  which  result.  in  substituting  other  constit- 
uents for  its  hydrogen.     When  ammonium  chloride  in  strong  water 
solution  is  acted  upon  by  chlorine,  nitrogen  chloride  is  produced  ; 

NH4C1  +  6C1  ^  NC13  +  4HCL 
•10 


132        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

A  similar  reaction  probably  takes  place  with  bromine  and  iodine,  pro- 
ducing NBrs  and  NI3.  These  substances  are  extremely  explosive, 
among  the  most  violent  'known,  and  consequently  very  dangerous  to 
handle.  Dulong  discovered  the  nitrogen  chloride  (1811),  and  lost  an  eye 
and  three  fingers  in  preparing  it,  and  later  Faraday  and  Sir  Humphry 
Davy  were  injured  by  its  explosion. 

340  Similarly  by  reaction  between  ammonia  gas  and  heated  metal, 
compounds  are  produced  in  which  the  metal  appears  to  be  substituted 
for  the  hydrogen  of  the  ammonia.  Thus  with  sodium  are  obtained 
the  compounds  NaH2N  and  Na3N.  These  with  water  yield  sodium 
hydroxide,  NaOH,  and  ammonia,  NHS.  Some  metals  form  nitrides 
by  direct  combination  with  nitrogen — e.  g.,  magnesium,  which  forms 
Mg8N2,  and  the  latter  yields  ammonia  by  contact  with  water. 

34:1  Hydrazine  is  a  second  compound  of  nitrogen  and  hydrogen.  It  has 
the  formula  N2H4,  and  is  a  gas  of  pungent  odor.  It  is  very  hygroscopic, 
forming  with  water  a  stable  compound,  N3H4H20.  The  latter  is  a  very 
corrosive  liquid,  which  acts  as  a  base  in  forming  salts— e.  g.,  N2H4HC1. 

342  Hydroxylamine,  NH2OH,  in  water  solution  acts  also  as  a  base,  and, 
like  ammonia  and  hydrazine,  combines  with  acids  additively — e.  g., 
NHaOH-HCl. 

343  Hydrazoic  acid.* — Most  remarkable  is  this  compound  of  nitrogen 
and  hydrogen,  HN8,  which  acts  as  an  acid.    It  is  a  clear  liquid  (boiling 
point,  37°),  very  explosive,  soluble  in  water,  and  of  intolerable  odor. 
The  sodium  salt,  NaN8,  is  soluble,  and  the  silver  salt,  AgN3,  is  insoluble, 
and  both  are  explosive.     A  singular  reaction  is  with  ammonia,  thus : 

NH8  +  HN3  =  NH4N3. 

One  hydride  of  nitrogen,  acting  as  a  base,  combines  with  another 
hydride  of  nitrogen  which  acts  as  an  acid,  forming  a  salt  whose  com- 
position is  N4H4,  or,  reduced  to  simplest  terms,  NH.  This,  too,  is 
explosive. 

With  hydrazine  also  this  acid  combines  additively,  giving  the  salt 
N3H4HN3,  or  N6H6,  and  this  is  extremely  explosive. 

6j.  The  Relation  of  Nitrogen  to  Living  Things 

344  It  has  already  been  stated  that  this  element  is  an  essential  constitu- 
ent of  the  plant  and  animal  organism.    Indeed,  it  is  one  of  the  elements 
in  that  fundamental  form  of  living  matter  called  protoplasm  (see  No. 
191).     It  seems  very  probable  that  the  extreme  instability  or  change- 

*  Curtius,  1891, 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    133 

fulness  of  those  substances  which  are  most  intimately  associated  with 
vital  activities  is  due  in  large  measure  to  the  characteristics  imparted 
by  the  constituent  nitrogen.  It  is  also  an  element  in  the  rejected  waste 
products  of  the  animal.  Therefore  its  supply  must  be  renewed,  and  it 
becomes  an  essential  constituent  of  food. 

The  higher  animals,  including  man,  although  they  live  in  an  atmos-  345 
phere  which  is  four  fifths  free  nitrogen  and  are  constantly  drawing  this 
into  the  lungs,  are  wholly  unable  to  use  any  of  this  nitrogen  as  food. 
They  can  not  even  use  nitrates  nor  ammonium  salts  as  a  source  of  this 
element.  They  must  have  it  already  as  a  constituent  with  carbon  and 
other  elements  in  the  organic  foods.  Such  compounds  are  found  par- 
ticularly in  meat,  in  fish,  and  in  portions  of  those  foods  which  come 
from  plant  seeds,  such  as  wheat  and  other  grains.  The  higher  animal^ 
are  therefore  ultimately  dependent  on  the  plant  for  nitrogenous  food, 
and  it  becomes  of  special  interest  to  learn  whence  the  plant  obtains  its 
supply  of  nitrogen. 

In  contrast  with  the  animal,  the  plant  takes  its  nitrogenous  food  in  346 
the  form  of  ammonia  and  of  nitrates  which  it  finds  in  the  soil.  These 
substances  come  into  the  soil  in  limited  quantities,  derived  from  the 
decay  of  nitrogenous  organic  matter  which  finds  its  way  there.  This 
produces,  first,  ammonia,  and  then  nitrate,  by  nitrification,  the  process 
being  itself  dependent  on  bacterial  life  (see  No.  328).  They  may  also 
come  to  some  extent  from  the  atmosphere,  washed  down  by  rain.  But 
a  soil  may  lose  its  fertility  through  exhaustion  of  its  nitrogenous  food 
by  the  removal  of  crops ;  therefore  this  is  restored  artificially  by  the  use 
of  fertilizers,  such  as  manures  and  crude  ammonium  salts  and  nitrates. 

There  has  been  much  investigation  as  to  whether  the  nitrifying  bac-  347 
teria  of  the  soil  are  able  to  draw  and  do  draw  upon  the  atmosphere  for 
their  supply  of  nitrogen  as  they  do  for  oxygen.  The  evidence  seems  to 
show  that  they  do,  and  that  in  this  manner  atmospheric  nitrogen  ulti- 
mately reaches  the  plant  as  food.  Combined  nitrogen,  therefore,  is 
valuable,  being  one  of  the  most  costly  of  food  constituents.  This  has 
led  to  many  attempts  to  manufacture  nitrogenous  compounds  cheaply 
from  the  nitrogen  of  the  air,  but  so  far  they  have  not  been  commer- 
cially successful. 

The  relation  of  combined  nitrogen  in  the  soil  to  the  food  supply  of    348 
wheat-consuming  peoples  has  attracted  much  attention.     Sir  William 
Crookes*  has  reckoned  that  should  all  the  land  available  for  growing 
wheat  be  in  use,  and  the  present  average  rate  of  production  be  main- 

*  Address  as  President  of  the  British  Association  for  the  Advance- 
ment of  Science,  1898.    Chemical  News,  September  9,  1898. 


134        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

tained,  the  total  wheat  produced  would  suffice  to  supply  food  to  the 
naturally  increasing  population  of  bread-eaters,  at  the  present  rate  of 
consumption,  only  until  the  year  1931.  Furthermore,  he  estimates 
that  the  present  acreage  could  meet  this  increased  demand  made  by 
increase  of  population  if  the  average  yield  of  wheat  per  acre  could  be 
raised  from  the  present  quantity,  12.7  bushels,  to  20  bushels.  From 
results  obtained  on  the  experimental  farm  at  Rothamstead,  he  calcu- 
lates that  this  could  be  done  by  the  use  as  fertilizer  of  about  twelve 
million  tons  annually  of  sodium  nitrate  distributed  over  the  World. 
But  the  present  output  of  this  substance  is  only  about  one  and  a  quar- 
ter million  tons.  He  then  considers  the  possibility  of  producing  nitrate 
by  electricity — that  is,  causing  the  nitrogen  and  oxygen  of  the  air  to 
combine  by  electric  discharge.  From  experiments  by  Lord  Rayleigh, 
he  calculates  that  one  ton  of  sodium  nitrate  would  cost  $130,  made  by 
electricity  from  steam  power,  but  only  $25  if  from  water  power,  as  at 
Niagara. 

349  In  the  same  connection  he  calls  attention  to  the  enormous  quantity 
of  combined  nitrogen  which  is  thrown  away  in  the  sewage  and  refuse 
of  towns  and  cities,  estimating  its  value  for  the  United  Kingdom  alone, 
if  it  could  be  recovered,  as  $80,000,000  per  year. 

7.  OXYGEN 

0.-15.88 

350  History.— Oxygen  was  discovered   August   1,  1774,  by  Priestley, 
who  made  it  by  heating  mercuric  oxide,  HgO.     It  was  also  discovered 

•  independently  by  Scheele,  a  Swede,  at  nearly  the  same  time.  As  early 
as  1675  Mayow,  an  Englishman,  partly  anticipated  these  more  definite 
discoveries  by  recognizing  some'  of  the  peculiarities  of  air,  now  known 
to  be  due  to  oxygen.  Lavoisier  named  the  gas  oxygen,  signifying  the 
acid-producer. 

351  Natural  occurrence.— Of  the  elements  of  the  earth,  oxy- 
gen is  the  most  abundant  and  the  niost  generally  dis- 
tributed.   Uncombined  it  makes  up  more  than  one  fifth  of 
the  atmosphere,  while  combined  it  constitutes  eight  ninths 
of  all  water  and  about  one  half,  it  is  estimated,  of  the 
earth's  crust,  including   compounds  with  almost  all  the 
other  elements. 

352  Preparation.— It  is  not  practicable  to  remove  the  nitro- 
gen from  air  and  thus  obtain  the  oxygen ;  other  and  less 


JOSEPH  PRIESTLEY 

B.  England,  1733.     D.  Pennsylvania,  1804. 

(See  Nos.  306,  350,  388.) 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    135 

direct  methods  are  used.  It  is  made  (1)  by  the  electrolysis 
of  acidulated  water  (see  No.  202) ;  (2)  by  heating  some 
metallic  oxides — e.  g.,  mercuric  oxide  and  manganese  di- 
oxide; (3)  by  heating  potassium  chlorate,  KC103,  or,  pref- 
erably, a  mixture  of  this  salt  with  manganese  dioxide, 
which  evolves  oxygen  at  a  lower  temperature  than  either 
when  alone.  Potassium  chloride,  KC1,  is  the  other  product 
of  this  reaction.  This  is  the  most  common  laboratory 
method,  and  it  is  also  applied  commercially  for  the  prep- 
aration of  oxygen.  (4)  Another  method,  which  is  applied 
on  a  large  scale  in  England,  consists  in  heating  barium  di- 
oxide, Ba02,  under  reduced  pressure.  Oxygen  is  thus  lib- 
erated, and  the  monoxide,  BaO,  is  left.  This  in  turn  is 
heated  with  air  under  increased  pressure,  and  the  dioxide 
is  reproduced.  The  oxygen,  therefore,  comes  from  air,  and 
the  barium  oxide  serves  as  carrier. 

Oxygen  comes  into  commerce  stored  under  pressure  in 
metallic  cylinders. 

Properties. — The  gas  is  without  color,  odor,  or  taste,  and  353 
is  heavier  than  air  in  the  ratio  of  15.9  to  14.4.  Under  the 
pressure  of  fifty  atmospheres  and  at  —118°  it  condenses  to 
a  liquid  which  boils  at  —183°  (Dewar),  and  at  a  still  lower 
temperature  solidifies.  One  hundred  volumes  of  water  dis- 
solve 3.1  volumes  of  the  pure  gas  at  20°  and  760  millimeters,' 
but  only  0.6  of  a  volume  from  the  air,  since  the  latter  is 
only  one  fifth  oxygen. 

Oxygen  is  a  very  reactive  substance  ;  binary  compounds  354 
of  it  are  known  with  all  the  other  elements  except  fluorine, 
bromine,  argon,  and  helium.  With  most  of  these  it  com- 
bines directly,  with  some  at  ordinary  temperature,  and  with 
some  only  at  high  temperature.  The  phenomenon  of  com- 
bustion has  already  been  described  in  other  connections, 
and  oxygen  has  been  called  a  supporter  of  combustion. 
But  the  term  is  purely  relative.  Oxygen  and  air  may  be 
burned  in  an  atmosphere  of  combustible  gas,  and  thus  the 
relative  positions  be  reversed. 


136        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

355  The  oxides  are  of  three  kinds :  those  which  are  acid- 
forming,  those  which  are  base-forming,  and  those  which  are 
neutral — that  is,  which  act  neither  as  base  nor  acid.     There 
are  some  which  act  as  bases  in  some  compounds  and  as 
acids   in  others — e.  g.,   zinc   oxide,  ZnO,  and  aluminium 
oxide,  A1203.     Carbon  monoxide  is  neutral,  and  many  illus- 
trations have  already  been  given  of  the  acid  and  basic  oxides. 

356  Oxygen  not  only  supports  combustion,  but  it  is  neces- 
sary to  life,  at  least  in  the  higher  forms.     In  the  animal  it 
is  absorbed  from  the  air  by  the  blood  and  carried  to  the  dif- 
ferent parts  of  the  organism,  where  it  effects  the  oxidation 
of  various  substances,  and  so  supplies  heat  and  energy  to 
the  system.     When  breathed  for  a  short  time  pure — that 
is,  undiluted  by  nitrogen — it  acts  as  a  tonic,  but  if  breathed 
longer  it  becomes  harmful,  producing  fever  and  weakness ; 
and  if  inhaled  pure  and  under  increased  pressure,  it  acts 
as  a  poison.     It  is  of  great  service  in  some  diseases,  when 
the  ordinary  air  is  not  rich  enough  in  oxygen  to  serve  its 
purpose ;  also  to  sustain  life  in  diving-bells  and  submarine 
vessels,  and  in  balloon  ascensions  to  the  higher  atmosphere 

357  which  is  too  rarefied  to  support  human  life.     It  is  also  used 
in  the  oxyhydrogen  flame  for  high  temperatures,  which 
finds  application  in  the  calcium  light.     Its  use  is  found 
advantageous  in  the  purification  of  coal  gas,  in  the  bleach- 
ing of  paper  pulp,  in  the  thickening  of  oils  for  varnishes, 
etc.     It  has  been  attempted,  and  with  some  success,  to  sup- 
.ply  a  high-grade  illuminating  gas  by  mixing  from  15  to  30 
per  cent  of    oxygen  with  the  hydrocarbon  gas  which  is 
made  by  destructive  distillation  (T.  E.  Thorpe). 

7a.   Ozone,  03 

358  When  electric  sparks  pass  through  air,  or  through  pure 
oxygen,  or,  still  better,  when  the  passage  is  by  what  is  called 
the  silent  discharge,  the  gas  is  found  to  have  a  peculiar 
odor  and  to  be  capable  of  oxidizing  mercury  and  other  sub- 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS  137 

stances  which  are  not  thus  acted  upon  by  oxygen  at  ordi- 
nary temperature.  The  substance  to  which  these  proper- 
ties are  due  is  named  ozone  (signifying  smell).  Contrac-  359 
tion  of  volume  accompanies  its  formation,  and  by  bringing 
this  about  in  pure  oxygen  and  measuring  the  contraction, 
then  removing  the  ozone  by  absorption  with  turpentine  or 
similar  substance,  and  measuring  the  second  contraction 
thus  produced,  it  has  been  found  that  the  latter  is  twice 
the  former  contraction.  Therefore,  three  volumes  of  oxy- 
gen are  converted  into  two  of  ozone,  and  the  two  volumes 
of  ozone  are  converted  into  three  of  oxygen  simply  by  heat- 
ing. Ozone,  then,  contains  nothing  but  oxygen — indeed,  it 
is  an  allotropic  form  of  the  latter.  From  the  foregoing  360 
facts  its  specific  gravity  should  be  (3  X  16)  -r-  2  =  24.  Of 
the  oxygen  used,  not  more  than  20  per  cent  can  be  con- 
verted into  ozone,  hence  it  has  never  been  obtained  pure ; 
but  an  approximate  confirmation  of  the  calculated  specific 
gravity  has  been  deduced  from  its  rate  of  diffusion  (see  No. 
203/i,  Part  I),  which  is  nearly  the  same  as  that  of  carbon 
dioxide  (sp.  gr.  22). 

The  formation  of  ozone  accompanies  the  oxidation  of  361 
various  substances — e.  g.,  moist  phosphorus  and  certain 
resins,  also  the  burning  of  hydrogen  in  air;  hence  it  is 
generally  present  in  the  atmosphere,  but  only  in  small 
quantity — at  most  one  volume  in  about  700,000.  It  is 
more  abundant  in  the  air  of  the  country  and  the  seashore 
than  of  the  city ;  more  during  spring  than  during  summer 
or  winter ;  more  during  rainy  than  during  clear  weather, 
and  it  is  increased  by  thunderstorms  (Ramsay). 

Properties. — Ozonized  oxygen  seen  through  considerable  362 
depth  (one  meter  with  10  per  cent  of  ozone)  is  blue,  and, 
when  cooled  by  liquid  oxygen  to  —180°,  the  ozone  is  con- 
densed to  a  dark-blue  liquid  which  boils*  at  —119°.     In 
water  it  is  nearly  fifteen  times  more  soluble  than  oxygen, 

*  Troost,  Comptes  Rendus,  June,  1898. 


138        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

according  to  at  least  one  investigator,  but  the  statements 
on  this  point  are  contradictory.*  Its  formation  from  oxy- 
gen involves  the  absorption  of  30,000  calories.  When  it  is 
heated  to  250°  or  300°  it  is  converted  entirely  into  oxygen 
with  liberation  of  heat.  If  heated  quickly,  especially  if 
under  pressure,  it  explodes.  Contact  with  some  substances 
—  e.  g.,  copper  oxide  —  converts  it  into  the  original  quantity 
of  oxygen  without  other  change.  In  accordance  with  its 
363  endothermic  formation,  it  is  very  reactive,  acting  upon 
many  substances  as  a  powerful  oxidizer  at  ordinary  tem- 
perature. Some  substances  —  e.  g.,  turpentine  —  take  up  the 
whole  of  its  oxygen  ;  others  —  e.  g.,  metallic  mercury  and 
silver  —  combine  with  only  one  third  of  its  oxygen,  liberat- 
ing two  thirds  as  ordinary  oxygen  gas  : 

2Ag  (silver)  +  03  =  Ag20  +  02. 
Of  similar  nature  is  the  reaction  with  potassium  iodide  : 

SKI  +  03  +  H20  =  K2OH20  +  Ig  +  Og  . 
This  property  is  used  in  order  to  recognize  the  presence  of 
ozone,  for  litmus  paper  wet  with  potassium  iodide  solution 
turns  blue  on  exposure  to  ozone,  because  of  the  alkali  hy- 
droxide formed,  or,  if  starch  is  present,  the  liberated  iodine 
turns  the  starch  blue.  Curiously  enough,  ozone  may  also 
act  as  a  reducing  agent  on  substances  which  yield  oxygen 
readily.  Thus  : 


364  .       Ozone  is  irritating  to  inhale  in  considerable  quantity, 
and  fatally  poisonous  when  concentrated.     It  seems  to  act 
as  a  reducer  in  the  lungs,  since  the  blood  appears  as  it  does 
when   suffocation   has   taken   place   (Ramsay)  ;   still,  it  is 
somewhat  used  medicinally. 

365  NOTE.  —  Ozone  may  be  regarded  as  an  oxide  of  oxygen  or  as  an  ele- 
mentary polymer.     In  terms  of  the  atomic  theory,  its  molecule  is  said 
to  contain  three  atoms,  while  that  of  ordinary  oxygen  gas  contains  two 
atoms  of  oxygen.   0 

*  Mailfert,  Comptes  Rendus,  119  (1894). 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    139 

7b.  Hydrogen  Dioxide  or  Peroxide,  HZ0Z 

A  substance  greatly  resembling  ozone,  so  much  so  that  366 
they  can  not  always  be  distinguished,  is  hydrogen  dioxide, 
H202.  It  is  said  to  be  formed  in  small  quantity  by  reac- 
tion between  water  and  the  oxygen  which  the  former  holds 
in  solution  and  hence  to  be  present  in  natural  waters.  The 
chief  method  of  formation— the  one  used  in  making  the 
commercial  article — is  by  the  action  of  dilute  sulphuric 
acid  on  barium  dioxide  : 

Ba02  +  H2S04  =  BaS04  +  H202. 

The  barium  sulphate,  being  insoluble,  is  removed  by 
filtration  or  decantation,  and  the  dilute  solution  is  concen- 
trated by  evaporation  at  low  temperature.  A  solution  is  367 
obtained  which  has  the  specific  gravity  of  1.45  and  remains 
liquid  at  —30°.  It  has  a  pungent  odor  and  metallic  taste, 
and  is  very  unstable.  The  concentrated  solution  begins  to 
decompose  at  about  20°,  and  if  rapidly  heated  may  explode. 
Under  low  pressure  the  dioxide  volatilizes  at  about  84°, 
and  a  distillate  99  per  cent  pure  is  obtainable  (Wolffenstein, 
1894).  The  dilute  solution  is  more  stable,  but  by  heating 
it  is  entirely  decomposed  into  water  and  oxygen.  This 
decomposition  is  exothermic,  liberating  23,000  calories. 
Like  ozone,  it  is  an  active  oxidizer,  and  may  also  act  as  a 
reducer.  It  is  used  in  the  laboratory  as  a  reagent,  in  the 
arts  for  its  bleaching  property,  and  in  medicine  as  a  disin- 
fectant and  germicide. 

7c.    Water,  HZ0 

Cavendish  in  1781  was  the  first  to  show  that  water,  and  368 
water  alone,  is  formed  by  the  combustion  of  hydrogen  and 
oxygen.  Sir  •Humphry  Davy  in  the  early  years  of  the  cen- 
tury separated  water  by  electrolysis  into  hydrogen  and 
oxygen  solely.  Gay-Lussac  and  Humboldt  determined  its 
volumetric  composition  in  1805,  and  Berzelius  and  Dulong 


140        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

its  composition  by  weight  in  1820.  Since  then,  and  even 
in  recent  years,  as  stated  in  another  connection  (see  Nos. 
146  and  147,  Part  I),  many  have  investigated  its  exact  com- 
position. 

369  Water  is  the  most  abundant  compound  on  the  earth. 
Its  presence  on  the  planets  Mars  and  Venus  is  thought 
probable.     Besides  the  water  which  is  visible  as  such  is 
that  water  which  is  a  constituent  of  other  things  but  easily 
separable  from  them ;  for  example,  water  of  crystallization. 
In  this  sense  water  is  a  constituent  of  many  minerals  and 
of  both  the  plant  and  the  animal  organism.     In  plants  it 
constitutes  from  50  to  95  per  cent  of  their  weight,  and  the 
human   body  yields  by  drying  about  70  per  cent  of  its 
weight  as  water. 

Many  reactions  in  which  water  is  a  product  have  been 
already  described  in  other  connections,  and  they  do  not  call 
for  further  consideration. 

370  Properties. — Water  is  colorless,  save  when  seen  through 
a  considerable  depth,  and  it  then  shows  a  bluish-green  tint. 
This  is  seen  also  in  ice  and  water  vapor.     When  pure,  it  is 
without  taste  or  odor.     It  freezes  at  0°  and  boils  at  100° 
under  a  pressure  of  760  millimeters.     Increase  of  pressure 
lowers  the  freezing  point  and  raises  the  boiling  point.     It 
shows  its   greatest   density  at  4°,  when  by  definition   1 
cubic  centimeter  of  it  weighs  1  gram.    The  specific  grav- 
ity of  ice  at  0°  is  about  0.9 — that  is,  water  expands  on 
freezing.     In  the  fusion  of  1  gram  of  ice  at  0°  to  water  at 
0°,  80  calories  of  heat  are  absorbed.     In  converting  1  gram 
of  water  at  100°  into  vapor  at  the  same  temperature  537 
calories  are  absorbed.     Water  expands  more  than  any  other 
substance  in  vaporizing,  1  volume  of  the  liquid  becoming 
1,650  of  the  vapor.     It  has  also  the  highest  heat  capacity. 
It  is  a  poor  conductor  of  heat  and  electricity.     Its  forma- 
tion heat  is  68,400  calories. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS 


7d.  Natural  Waters 

Pure  water  is  an  artificial  product,  since  natural  water,  coming  in  371 
contact  with  the  atmosphere  and  the  earth,  takes  more  or  less  of  mat- 
ter into  solution,  and  ceases  to  be  pure  water  in  the  chemical  sense  of 
the  term.  That  which  comes  in  contact  with  the  atmosphere  only — 
that  is,  rain  water  (including  snow  and  hail) — is  consequently  the 
purest.  That  which  passes  over  the  surface  of  the  land  and  drains  into 
flowing  streams,  and  that  which  sinks  through  the  ground  and  comes 
to  the  surface  again  as  spring  or  well  water,  must  be  greatly  modified 
by  the  nature  of  the  matter  with  which  it  comes  in  contact.  More  or 
less  of  the  soluble  matter  thus  picked  up  is  carried  on  to  the  sea,  where 
it  accumulates ;  so  that  sea  water  contains  the  maximum  of  dissolved 
substances.  Rain  water  sometimes  shows  as'much  as  50  grams  of  solids  372 
dissolved  in  1,000,000  cubic  centimeters  of  water.  River  waters  vary 
greatly. in  the  quantity  of  solids  dissolved;  for  example,  in  1,000,000 
cubic  centimeters  of  water  the  river  Neva  contains  only  55  grams  of 
solids ;  the  Seine,  from  190  to  432 ;  the  Thames — in  its  upper  parts  387, 
at  London  from  400  to  450,  and  in  its  lower  parts  1,617 ;  the  St.  Law- 
rence, 170;  the  Nile,  1,580;  the  Jordan,  1,052.  Spring  waters  also  vary 
greatly.  If  solids,  especially  salts,  are  present  in  such  quantity  as  to 
give  marked  taste  and  sometimes  odor  to  the  water,  it  is  called  min- 
eral, and  may  be  used  medicinally,  even  if  not  acceptable  for  ordinary 
drinking.  For  the  latter  purpose  hardly  more  than  400  or  500  parts 
per  million  would  be  tolerated,  while  some  mineral  waters  contain  as 
much  as  20,000  or  even  30,000.  Sea  water  on  the  average  contains  of 
solids  about  36,000  parts  per  million. 

As  to  the  nature  of  the  impurities. — The  impurities  of  rain  water  are   3  73 
chiefly  ammonium  salts,  nitrates,  sodium  chloride  and  sodium  sulphate, 
dust,  and  germs,  besides  the  normal  gases  of  the  air.     Of  river  water, 
perhaps  the  most  abundant  mineral  impurities  are  calcium  carbonate 
and  sulphate. 

Mineral  waters  may  be  distinguished  according  to  their  content  as   374 
follows : 

Carbonated  waters,  containing  carbon  dioxide,  sometimes  so  much 
of  it  that  they  effervesce,  have  acid  taste,  and  action  on  litmus. 

Alkaline  waters,  containing  much  sodium  carbonate. 

Bitter  waters,  containing  especially  magnesium  salts. 

Chalybeate  waters,  containing  iron  acid  carbonate. 

Silirious  waters,  containing  alkaline  silicates  or  silicic  acid. 

Sulphur  waters,  containing  hydrogen  sulphide. 

Of 'sea  water,  sodium  chloride  (common  salt)  is  by  far  the  most 


142        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

abundant  impurity,  showing  25,000  parts  or  more  per  million.  Next 
in  abundance  are  magnesium  chloride  and  sulphate,  calcium  sulphate, 
and  potassium  chloride :  many  other  substances  are  present  in  minute 
quantity. 

375  Hardness. — Waters  are  called  hard  if  they  cause  precipitation  or 
turbidity  when  soap  solution  is  added  to  them,  and  soft  in  the  absence 
of  this  property.     The  soap  can  not  have  its  desired  cleansing  effect 
until  the  precipitation  ceases  and  the  soap  remains  in  solution.     Hard- 
ness, therefore,  since  it  causes  a  waste  of  soap,  is  in  this  respect  objec- 
tionable.    The  explanation  of  the  precipitation  is  as  follows :  Soap  is  a 

375/1  soluble  alkaline  salt,  the  base  of  which  is  sodium  hydroxide  (in  hard 
soap)  or  potassium  hydroxide  (in  soft  soap),  and  the  acids  of  which  are 
the  so-called  fatty  acids,  which  are  derived  from  fats  and  oils  and  of 
which  stearic  acid  may  be  taken  as  representative.  The  salts  of  these 
acids,  with  other  than  the  alkaline  bases,  are  insoluble  in  water.  Con- 
sequently, when  soap  solution  is  added  to  water  which  contains  non- 
alkaline  salts,  a  precipitate  appears  which  is  the  non-alkaline  salts  of 

375/2  the  fatty  acids.  The  phenomenon  of  hardness  is  due,  therefore,  to  the 
presence  in  the  water  of  non-alkaline  salts.  These  are  commonly  salts 
of  calcium  and  magnesium.  If  these  are  present  as  acid  carbonates, 
they  are  precipitated  by  boiling,  and  the  cause  of  hardness  is  thereby 

375/3  removed.  (See  No.  271,  Part  I.)  Hardness  which  is  due  to  non-alka- 
line acid  carbonates  is  called  temporary.  On  the  other  hand,  if  it  is 
due  to  non-alkaline  salts  other  than  carbonates,  it  is  not  removable  by 
boiling,  and  is  called  permanent. 

376  The  nature  of  the  impurities  in  water  has  important  bearing  also 
upon  its  suitability  for  industrial  uses,  such  as  brewing,  bleaching, 
dyeing,  and  the  processes  involved  in  making  textile  fabrics ;  in  paper- 
making  ;  in  tanning ;  in  sugar  refining.     For  use  in  steam  boilers,  sub- 
stances like  magnesium  chloride  and  free  acids,  which  cause  corrosion 
of  the  iron,  are  objectionable ;  also  those  which  cause  deposits  or  incrus- 
tations in  the  boilers,  such  as  calcium  and  magnesium  acid  carbonates 
and  calcium  sulphate. 

377  The  suitability  of  a  water  for  drinking  purposes  is  dependent  not 
only  on  its  freedom  from  excessive  impurities  of  the  kind  already  indi- 
cated, which  may  be  and  generally  are  present  in  small  quantity  in 
good  drinking  water,  but  also  on  the  absence  of  impurities  of  quite  a 
different  order — namely,  those  which  are  of  plant  or  animal  origin  and 
organic  in  nature — that  is,  those  which  contain  carbon,  and  often  nitro- 
gen, and  which  are  subject  to  putrefaction  or  decay ;  and  still  further 
on  the  absence  of  those  minute  living  organisms  called  bacteria.     Nat- 
ural waters  generally  contain  more  or  less  of  the  latter,  or  of  their  germs, 


DESCRIPTION  OP  ELEMENTS  AND  COMPOUNDS    143 

which  are  capable  of  developing  and  greatly  multiplying  in  favorable 
conditions.  Many  kinds  of  bacteria  are  quite  harmless,  but,  on  the 
other  hand,  some  greatly  dreaded  diseases,  notably  cholera  and  typhoid, 
are  undoubtedly  produced  by  germs,  and  very  often  are  transmitted  by 
the  drinking  water.  The  presence,  therefore,  of  disease-producing  377/1 
germs  has  come  to  be  recognized  as  a  possible  danger  in  a  water  sup- 
ply. Accompanying  the  excrement  of  the  diseased  body,  they  find 
their  way  into  the  soil  and  into  the  sewage,  and  thence  often  into  the 
drinking  water  itself.  Evidence,  therefore,  of  the  presence  in  water  of 
substances  which  are  not  likely  to  be  there  except  they  come  with  sew- 
age, even  if  the  substances  themselves  are  entirely  harmless,  is  evidence  377/2 
of  possible  danger,  since  the  germs  themselves  may  at  any  time  be 
present  in  the  water  if  once  they  reach  the  sewdge.  In  addition  to 
this,  it  is  probable  that  even  water  contaminated  with  organic  matter 
of  plant  origin  or  with  the  sewage  of  healthy  persons  may  cause  dis- 
eases such  as  diarrhoea,  to  say  nothing  of  the  disgusting  possibility  of 
drinking  dilute,  sewage,  even  though  it  be  without  harm. 

One  substance  which  almost  always  accompanies  refuse  matter  of 
animal  origin  is  sodium  chloride  (common  salt).  It  is  also  present  nor-  377/3 
mally  in  most  waters,  and  in  any  quantity  which  is  acceptable  to  the 
taste  is  entirely  harmless.  If,  however,  it  is  found  present  in  excess  of 
what  may  be  regarded  as  normal  in  a  given  sample,  it  is  reckoned  as 
giving  a  valuable  indication  of  probable  pollution  by  sewage.  The 
same  may  be  said  of  ammonia  and  of  nitrates  and  nitrites.  Ammonia  is  377/4 
produced  by  the  decomposition  of  nitrogenous  organic  matter,  whether 
by  the  slow  process  of  decay  or  by  the  quicker  processes  of  chemical 
reaction  ;  the  nitrates  and  nitrites  are  also  the  last  products  in  the  oxi- 
dation of  such  matter.  The  presence,  therefore,  of  these  substances 
beyond  their  normal  quantity  for  a  given  sample  of  water  gives  warn- 
ing of  probable  contamination.  Finally,  an  approximate  measure  may  377/5 
be  got  of  the  number  of  living  germs  which  water  contains  by  sow- 
ing a  small  measured  volume  of  the  sample  in  a  medium  suitable  for 
their  rapid  growth,  and,  after  a  sufficient  interval,  counting  the  visible 
growths.  Some  degree  of  success  has  been  reached  in  identifying  the 
specific  germs  of  certain  diseases,  but  the  chemical  indications  just 
mentioned  give  information  much  more  readily  than  those  which 
depend  on  the  actual  identification  of  germs. 

7e.  Purification  of  Water 

Filtration  on  a  small  scale   is  the   treatment   most   commonly    378 
employed  for  the  purification  of  drinking  water.    This  strains  out  mat- 


144:        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

ter  in  suspension,  and  renders  turbid  water  more  acceptable  in  appear- 
ance. But  clearness  is  no  test  at  all  of  purity ;  a  water  may  be  perfectly 
clear  and  at  the  same  time  most  dangerously  impure.  Many  filtering 
materials  are  in  use,  and  they  differ  widely  in  their  effects,  although 

379  they  may  all  serve  to  clarify.     Charcoal,  especially  animal  charcoal, 
removes  suspended  matter,  and  to  some  extent  organic  dissolved  mat- 
ter, and  reduces  the  temporary  hardness ;  but  it  does  not  remove  bac- 
teria.    Indeed,  by  furnishing  a  favorable  medium  for  their  growth  it 
may  actually  increase  them  and  itself  become  a  source  of  danger. 

380  Stone,  sand,  spongy  iron,  and  prepared  paper  are  proposed  for 
domestic  filters,  but  none  of  them  affords  any  protection  against  the 
danger  from  harmful  bacteria.     Porous  earthenware  or  unglazed  por- 
celain may  strain  out  the  bacteria  almost  completely,  but  it  loses  its 
efficiency  with  use.     Filters  of  this  kind  are  generally  supplied  in  the 
form  of  cones  or  cylinders,  through  which  water  is  forced  by  hydrant 
pressure  or  simply  by  atmospheric  pressure.     These  should  be  removed 
at  least  once  a  week,  cleaned,  and  heated  for  thirty  minutes  in  boiling 
water  or  in  an  oven  (Mason). 

381  Distillation  affords  the  most  perfect  purification  of  water,  but  it 
is  not  so  easily   available   for  domestic  use,  although   largely  used 
at  sea. 

382  Boiling  for  fifteen  or,  better,  thirty  minutes,  by  killing  the  bac- 
terial life,  affords  most  useful  protection  against  danger,  "  and  should 
be  invariably  resorted  to  in  case  of  waters  which  bear  any  suspicion  of 
sewage  contamination.     The  vapid  taste  of  the  boiled  water  may  be 
removed  by  passage  through  a  filter,  which,  however,  should  be  exclu- 
sively employed  for  this  purpose  and  not  for  filtering  unboiled  water  " 
(Frankland). 

383  The  purification  of  drinking  water  on  a  large  scale  for  city  sup- 
plies is  undertaken  in  some  places  with  good  results.     By  the  use  of 
large  settling   basins   and   of   extensive   filtering  beds  suitably  con- 

.  structed  of  gravel  and  sand,  the  public  water  supply  may  be  greatly 
improved.  Such  filtration  properly  conducted  is  found  to  remove  bac- 
teria almost  completely.  This  surprising  result  is  due  to  the  growth 
upon  the  sand  of  a  kind  of  slime  which  acts  as  a  filtering  membrane, 
and  the  sand  is  not  effective  until  this  formation  has  taken  place. 
Besides  straining  out  the  bacteria,  this  filtration  tends  to  nitrify  the 
organic  matter  and  thus  to  improve  still  further  the  condition  of  the 

384  water  (Mason).     In  some  places  a  small  quantity  of  alum  is  added  to 
water  which   contains  acid  carbonates.     A  slight   precipitate  of  the 
gelatinous  aluminium  hydroxide  is  thus  produced,  which  takes  the 
place  of  the  slime  above  referred  to,  and  permits  the  more  rapid  filtra- 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS 

tion  through  coarse  sand  with  the  same  desired  result.  At  the  same 
time  no  appreciable  quantity  of  alum  goes  into  the  filtered  water. 
There  can  be  no  reasonable  doubt  that  the  treatment  of  drinking  385 
water  on  the  large  or  on  the  small  scale  as  herein  described  is  capable 
of  furnishing,  as  proved  by  results,  a  valuable,  although  of  course  not 
complete,  protection  to  public  health  against  certain  diseases. 

The  purification  of  water  on  a  large  scale  for  industrial  purposes  386 
is  also  undertaken,  particularly  the  removal  of  temporary  hardness  and 
of  those  substances  which  cause  boiler  deposits.  The  common  method 
is  precipitation,  followed  by  filtration  or  subsidence.  As  precipitating 
material,  various  substances  are  used,  such  as  calcium  hydroxide  (lime- 
water),  sodium  hydroxide,  sodium  carbonate,  sodium  fluoride,  and 
sodium  aluminate. 

7f.  Action  of  Water  on  Lead  and  Zinc 

As  lead  pipes  are  very  commonly  used  to  convey  drinking  water,  387 
and  as  lead  compounds  are  poisonous  and  tend  to  accumulate  in  the 
body,  it  becomes  an  important  sanitary  matter  to  know  whether  lead 
may  be  carried  into  the  water  by  contact  with  the  pipes.  That  some 
varieties  of  natural  waters  do  corrode  the  lead,  and  that  many  instances 
of  poisoning  have  been  thus  caused,  is  not  to  be  doubted.  That  other 
varieties  do  not  attack  the  lead  is  also  true.  Hard  waters,  especially 
those  containing  acid  carbonates,  do  not,  as  a  rule,  take  up  lead ;  nor 
do  all  waters  without  acid  carbonates  act  upon  it,  but  many  certainly 
do  so  act.  The  fact  with  regard  to  a  given  sample  is  best  ascertained 
by  direct  experiment.  So  small  a  quantity  of  lead  as  0.7  parts  per 
million  of  water  is  reckoned  as  unwholesome  for  continued  use  (Frank- 
land). 

Zinc  also  is  acted  upon  by  many  waters,  but  the  quantity  taken  up 
is  small,  and  its  presence  is  not  regarded  as  serious.  Copper  should 
not  be  used  in  contact  with  drinking  water,  for  it  is  easily  corroded 
and  is  poisonous.  Tin  is  the  least  acted  on  of  the  available  metals. 

B.  THE  ATMOSPHEEE 

The  atmosphere  is  the  gaseous  envelope  which  surrounds  the  earth.  388 
In  the  ancient  Greek  philosophy  of  Aristotle,  air,  earth,  water,  and  fire 
were  the  four  elementary  principles  out  of  which  were  made  all  sub- 
stances. Boyle  in  the  seventeenth  century  was  one  of  the  first  to  in- 
vestigate scientifically  the  nature  of  air;  but  the  discovery  of  nitrogen 
by  Rutherford  in  1772,  and  of  oxygen  by  Priestley  in  1774,  alone  made 


14:6        ELEMENTARY  PRINCIPLES  OP  CHEMISTRY 


possible  the  explanation  of  the  true  nature  of  air  which  was  put  forth 
by  Lavoisier  in  1777.  The  quantitive  relation  between  the  oxygen  and 
nitrogen  was  established  in  1781  by  Cavendish. 


390 


FIG.  4. — Priestley's  apparatus  for  the  investigation  of  air  and  other  gases. 

Various  estimates  have  been  made  of  the  distance  above 
the  earth  to  which  the  atmosphere  extends.  From  obser- 
vations of  twilight  its 
height  has  been  cal- 
culated as  about  fifty 
miles.  With  this  height 
it  bears  the  relation  to 
the  earth  that  a  film 
one  twelfth  of  an  inch 
in  thickness  bears  to  a 
globe  one  foot  in  di- 
ameter (Koscoe).  Its 

FIG.  5. — Lavoisier's  apparatus  for  examm-  .  ;  ' 

ing  air  by  heating  a  volume  inclosed  in       weight    IS    SUCh    as    to 
a  retort  and  in  contact  with  mercury.  make  a  pressure  which 

is  variable,  but  which 

averages  1033.3  grams  per  square  centimeter  at  the  sea's 
level  (about  15  pounds  to  the  square  inch).     This  is  equal 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   147 

to  the  weight  of  a  column  of  mercury  1  square  centimeter 
in  section  and  760  millimeters  high  (=29.9  inches). 

The  atmosphere  is  a  mixture  in  which  the  nitrogen  and  391 
oxygen  so  greatly  exceed  the  other  substances  in  quantity 
that  it  is  customary  to  speak  of  air  as  made  up  of  these 
two  gases.  But  besides  these  there  are  present  argon, 
water,  carbon  dioxide,  nitric  acid,  ammonia,  ozone,  hydro- 
gen (according  to  Gautier,  C.  E.,  November,  1898,  1.5  parts 
in  10,000),  hydrogen  dioxide,  complex  organic  substances, 
and  dust,  including  the  germs  of  living  organisms.  All  of 
these  may  be  easily  removed  except  the  nitrogen,  oxygen, 
and  argon ;  and,  considering  the  mixture  of  these  three  for 
the  moment  as  air,  it  may  be  stated  that  one  liter  of  it  392 
weighs  1.293  grams  at  0°  and  760  millimeters,  which  is  14.40 
times  the  weight  of  the  same  volume  of  hydrogen.  In 
such  free  air  the  ratio  of  nitrogen  (including  argon)  to 
oxygen  is  remarkably  constant,  as  found  by  analysis  of 
samples  collected  over  land  and  over  sea,  at  widely  sepa- 
rated points  of  the  globe,  on  the  tops  of  mountains,  and  at 
the  greatest  height  reached  by  balloons.  The  greatest 
variation  is  only  about  1  part  in  200.  The  nitrogen  (in- 
cluding argon)  averages  79.04  and  the  oxygen  20.96  per 
cent  by  volume,  or  by  weight  77  and  23  per  cent  respect- 
ively. Nevertheless,  in  some  exceptional  instances  of  free 
air  and  in  the  air  of  confined  spaces,  such  as  buildings  and 
mines,  the  oxygen  has  been  found  to  vary  beyond  the  limit 
first  mentioned,  falling  as  low  as  20.26-  per  cent  in  mines. 
It  has  been  thought  by  some  that  at  extreme  heights  the  393 
air  may  be  slightly  richer  in  nitrogen  owing  to  the  slight 
difference  in  the  specific  gravity  of  the  two  gases,  but  this 
does  not  seem  to  be  established  by  evidence.  A  sample  of 
air  collected  at  the  height  of  15,500  meters  (51,000  feet)  by 
means  of  an  "  aerophile  "  in  February,  1897,  gave  20.79  per 
cent  of  oxygen  by  volume  and  79.21  per  cent  of  nitrogen, 
including  argon  (Cailletet).* 

*  Comptes  Rendus,  March  8,  1897, 


148        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

394  Air  a  mixture. — That  the  nitrogen  and  oxygen  are  free 
and    not  combined    in  air    is    proved    by  the  following 
facts : 

(!)•  Their  relative  quantity  is  subject  to  slight  but  un- 
mistakable variation. 

(2)  The  density  of  air  is  equal  to  the  mean  density  of 
the  two  gases,  reckoned  in  their  respective  quantities. 

(3)  Each  substance  dissolves  in  water  according  to  its 
own  degree  of  solubility,  and,  since  oxygen  is  considerably 
more  soluble  than  nitrogen,  air  which  is  dissolved  in  water 
is  richer  in  oxygen  than  is  undissolved  air,  the  proportion 
of  oxygen  by  volume  being  increased  from  21  to  35  per  cent. 
It  is  upon  this  dissolved  oxygen  that  fishes  and  other  gill- 
breathing  animals  depend. 

(4)  By  drawing  air  through  a  rubber  membrane,  the 
proportion   of  oxygen   may  be  increased  to  42  per  cent 
(Graham). 

(5)  Nitrogen  and  oxygen  may  be  mixed  in  their  due 
proportions  without  evolution  of  heat  or  change  of  volume, 
and  the  mixture  shows  all  the  properties  of  air. 

(6)  Air  may  be  liquefied,  and  even  frozen,  and,  when 
the  temperature  of  the  mixture  is  allowed  to  rise  slowly, 
the  nitrogen,  having  the  lower  boiling  point  (  —  194°),  vola- 
tilizes first,  and  soon  the  liquid  becomes  nearly  pure  oxygen 
—boiling  point  —183°. 

395  Liquefaction  of  air. — Air  was  liquefied  in  1883,  but  only  in  small 
quantity.     Quite  recently  the  process  has  been  operated   on  a  very 
much  larger  scale  and  more  cheaply,  so  that  it  has  been  proposed  to 
make  liquid  air  a  commercial  article,  and  to  apply  it  to  a  great  variety 
of  purposes.     In  Dewar's  method  of  liquefaction  the  gas  is  put  under 
pressure  of  120  to  140  atmospheres,  and  passed  through  coils  of  copper 
pipe  which  are  inclosed  in  a  vessel  whose  walls  are  protected  against 
the  passage  of  heat  by  layers  of  non-conducting  material.     The  coils 
are  cooled  to  —80°  by  solid  carbon  dioxide.    The  gas  thus  brought  to 
this  low  temperature  is  allowed  to  escape  through  a  small  hole,  and  its 
sudden  expansion  still  further  reduces  the  temperature  of  the  escaping 
gas  which  is  conducted  over  the  coils.    By  this  means  the  gas  con- 


DESCRIPTION  OF   ELEMENTS  AND  COMPOUNDS    149 

tained  in  the  latter  is  reduced  to  lower  and  lower  temperatures,  until  it 
liquefies  and  drops  into  a  receiving  vessel.  This  is  protected  against 
access  of  heat  by  a  double  wall,  the  space  between  the  two  walls  being 
vacuous. 

C.  ARGON 

The  next  constituent  of  the  atmosphere  following  nitrogen  and  396 
oxygen  in  quantity  is  argon.  It  was  not  discovered  until  1894,  having 
been  previously  reckoned  and  identified  with  the  nitrogen,  although 
Cavendish,  in  his  investigation  of  the  ratio  of  nitrogen  to  oxygen,  sug- 
gested the  possibility  that  something  other  than  nitrogen  was  present 
in  small  quantity.  In  an  elaborate  investigation  of  the  density  of 
gases,  Lord  Rayleigh  determined  with  great  accuracy  the  weights  of 
equal  volumes  of  nitrogen  obtained  from  air  by  removal  of  the  oxygen, 
and  of  nitrogen  obtained  by  five  different  chemical  reactions,  with  the 
following  results : 

Nitrogen  by  chemical  Nitrogen  from 

decomposition.  air. 

2.3001  grams.  2.3103 

2.2990      "  2.3100 

2.2987      "  2.3102 

2.2985      "  Mean,  2.3102 
2.2987      " 
Mean,  2.2990      " 

The  means  showed  a  difference  considerably  larger  than  any  proba- 
ble error  of  determination,  and  this  led  him  to  suspect  the  presence  of  a 
heavier  gas  with  the  atmospheric  nitrogen.  Associated  with  Professor 
Ramsay  he  passed  the  nitrogen  from  air  over  hot  magnesium,  which 
takes  up  nitrogen,  and  thus  obtained  a  small  quantity  of  gas  which 
would  not  combine  with  magnesium  nor  with  oxygen  by  the  electric 
spark.  This  was  the  new  element  which  they  named  argon  (signifying 
inactive).  It  has  since  been  found  occluded  by  several  minerals  and  a 
meteorite  and  dissolved  in  some  mineral  waters.  It  is  present-  in  air  to 
the  extent  of  1  volume  in  100,  and  therefore  the  percentage  of  true 
nitrogen  must  be  reduced  to  78.  (Argon  =  0.94  %  of  air,  Schloesing.) 

The  gas  condenses  to  a  liquid  which  boils  at  - 187°,  and  solidifies  to  397 
white  crystals  which  melt  at  —190°.  One  hundred  volumes  of  water 
dissolve  about  four  of  the  gas,  which  gives  it  about  the  same  solubility 
as  oxygen.  Its  specific  gravity  is  19.81  (Ramsay,  December,  1898). 
All  of  the  many  attempts  to  make  it  enter  into  combination  have 
failed  ;  its  chemical  properties  other  than  this  are  therefore  unknown, 


150        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

According  to  Gay-Lussac's  law  its  combining  weight  should  be 
19.81,  but  certain  physical  properties  which  it  possesses  are  thought  by 
some  to  indicate  39.62  as  the  proper  value. 

Other  New  Elements  in  the  Atmosphere 

398  Ramsay  has  stated  that  he  has  succeeded  in  separating  other  gase- 
ous substances  from  air,  which,  at  the  present  stage  of  investigation, 
appear  to  be  elements  hitherto  unknown.     They  may  suitably  be  men- 
tioned in  connection  with  argon  and  air,  although  their  general  prop- 
erties have  not  been  sufficiently  determined  to  permit  of  full  descrip- 
tion, nor  indeed  has  their  existence  been  established  beyond  doubt. 

Neon  (signifying  new)  is  the  name  given  to  one  of  these.  It  was 
obtained  by  liquefying  18  liters  of  atmospheric  argon  by  means  of 
liquid  air,  and  subjecting  the  liquid  to  fractional  distillation.  Sep- 
arating the  more  volatile  portion  and  redistilling  it,  Ramsay  finally 
(1898)  obtained  a  gas  having  a  specific  gravity  of  about  9.5  (H  =  1)  and 
more  volatile  than  nitrogen  and  argon,  and  differing  from  them  also  in 
other  properties.  He  estimates  its  quantity  as  1  volume  in  40,000 
volumes  of  air.  Like  argon,  it  shows  certain  physical  properties  which 
lead  some  to  the  conclusion  that  19.0  rather  than  9.5  should  be  reck- 
oned as  its  combining  weight  (Chemical  News,  September  23,  1898). 

399  The  same  investigator  thinks  he  has  evidence  of  three  additional 
gases  in  the  less  volatile  portions  of  the  liquid,  which  consisted  in  the 
main  of  argon,  all  coming  from  the  atmosphere.     These  he  has  named 
krypton  (signifying    hidden),   metargon,  and    xenon    (signifying    the 
stranger).     They  are  present  in  still  less  quantity  than  the  neon.     To 
metargon  he  gives  a  specific  gravity  about  the  same  as  that  of  argon. 
The  evidence  seems  not  yet  sufficient  to  establish  the  existence  and  ele- 
mentary nature  of  these  three  substances  (December,  1898). 

400  Helium  is  the  name  given  to  a  substance  which,  on  the  evidence  of 
the  spectroscope,  was  supposed  to  be  present  in  the  sun.     After  the 
discovery  of  argon  in  1894,  Ramsay  found  this  substance — i.  e.,  argon 
— present  in  a  gas  which  is  obtained  from  certain  minerals  and  which 
had  previously  been   regarded   as   nitrogen.     In   so  doing  he  found 
(March,  1895)  still  another  gas,  the  spectrum  of  which  was  identified 
with  that  of  helium.     The  presence  of  the  latter  substance  on  the  earth 
had  not  before  been  noted.     Then,  in  December,  1898  (see  Chemical 
News,  January  27,  1899),  he  found  helium  with  neon  in  the  crude  argon 
from  air.     It  has  also  been  found  in  a  number  of  minerals  and  mineral 
waters,  and,  like  argon,  in  a  meteorite.     Its  specific  gravity  (H  =  1)  is 
1.98  (Ramsay,  January,  1898).     As  in  the  case  of  argon,  no  attempts  to 
make  it  enter  into  combination  have  succeeded.    It  shows  the  same 


DESCRIPTION  OF.  ELEMENTS  AND  COMPOUNDS   151 

physical  property  which  is  possessed  by  argon,  neon,  and  metargon,  and 
this  fact  leads  some  to  think  that  its  combining  weight  also  should  be 
taken  as  twice  the  specific  gravity. 

Its  boiling  point  is  about  the  same  as  that  of  liquid  hydrogen 
(Dewar,  1898),  and  it  dissolves  in  water  to  the  extent  of  7  volumes 
in  1,000. 

8.  FLUORINE 

F.— 18.91 

Natural  occurrence.— Fluorine  was  first  isolated  in  1886  401 
by  Moissan.  It  is  found  in  nature  only  in  combination.  Its 
compound  with  calcium,  CaF2,  is  known  asfluorite  or  fluor 
spar,  and  is  quite  abundant.  Cryolite,  AlF3(NaF)3,  is 
brought  in  large  quantities  from  Greenland.  Combined 
fluorine  also  occurs  minutely  in  bone,  blood,  the  enamel  of 
teeth,  and  in  sea  and  mineral  water. 

Preparation.— Moissan  obtained  it  by  electrolyzing  in  a  402 
tube   made  of  platinum  and  iridium,  and  at   a  low  tem- 
perature (  —  23°),  pure  anhydrous  hydrogen  fluoride,  HF, 
mixed  with  potassium  fluoride,  KF. 

Properties. — It  is  described  as  a  greenish-yellow  gas  of  403 
a  peculiar  odor,  probably  due  to  the  formation  of  ozone 
when  fluorine  comes  in  contact  with  moisture.  It  condenses 
at  the  temperature  of  boiling  liquid  air  to  a  clear  yellow 
liquid,  which  boils  at  —  187°,  does  not  solidify  at  —  210°, 
has  a  density  of  1.14  (water  —  1),  and  is  soluble  in  all  pro- 
portions in  liquid  air  and  oxygen. 

The  gas  at  ordinary  temperature  combines  with  hydro-  404 
gen  explosively,  and  attacks  substances  which  contain  hy- 
drogen, forming  hydrogen  fluoride  or  hydrofluoric  acid, 
HF.  From  water  it  liberates  oxygen  as  ozone.  Indeed,  it 
combines  with  nearly  all  the  elements,  and  at  lower  tem- 
perature and  with  more  energy  than  does  oxygen.  It  is 
the  most  reactive  substance  known,  and  its  properties  make 
it  extremely  dangerous.  With  oxygen  no  compound  has 
been  obtained.  Keduced  in  temperature  to  —190°,  it  does 


152       ELEMENTARY  PRINCIPLES  OP  CHEMISTRY 

not  react  with  carbon,  water,  mercury,  glass,  nor  some 
other  substances  ;  but  it  still  reacts,  accompanied  by  incan- 
descence, with  hydrogen  and  with  hydrocarbons  like  tur- 
pentine. In  the  course  of  the  experiments  which  gave  these 
remarkable  results  some  drops  of  liquid  fluorine  fell  upon 
the  floor,  instantly  setting  the  wood  on  fire  (Moissan  and 
Dewar,  November,  1897). 

405  Hydrofluoric  acid  is  made  by  the  action  of  sulphuric  acid 
on  a  fluoride — e.  g.,  calcium  fluoride,  CaF2 : 

CaF3  +  H2S04  =  CaS04  +  2HF. 

406  It  is  a  colorless,  fuming  liquid,  boiling  at  19°.     The 
density  of  the  gas,  slightly  above  19°,  indicates  the  formula 
H2F2 ,  but  at  100°  it  indicates  HF.     It  is  one  of  the  most 

.  corrosive  substances  known.  As  a  gas  it  is  intensely  poi- 
sonous to  inhale,  and  in  contact  with  the  skin  it  produces 
most  painful  sores.  Those  dealing  with  it  protect  them- 
selves with  rubber  gloves  and  apron.  It  dissolves  most  of 
the  metals,  forming  salts — the  fluorides — and  it  dissolves 
also  the  substance  of  rocks,  like  sand  and  granite,  which 
is  a  silicate.  It  also  attacks  glass,  which  is  an  artificial 
silicate,  forming  with  the  silicon  a  gaseous  silicon  fluoride, 
SiF4 ,  hence  its  use  in  etching.  It  is  very  soluble  in  water, 
and  its  solution  comes  into  commerce  stored  in  bottles  of 
rubber  or  of  ceresine  (a  natural  paraffin). 

9.  SODIUM 

Na.— 22.88 

407  History. — The  element,  sodium,  was  separated  from  caustic  soda, 
its  hydroxide,  by  Davy  in  1807.    It  was  a  remarkable  discovery,  as  the 
caustic  soda  had  been  regarded  as  elementary. 

408  Natural  occurrence, — The  element  is  not  found  free,  but 
occurs  abundantly,  chiefly  in  the  chloride,  common   salt. 
This  is  found  in  sea  water,  constituting  about  three  per 
cent  of  the  same ;  also  in  mineral  waters,  and  in  extensive 


SIR   HUMPHRY    DAVY 

B.  England,  1778.     D.  1829. 

(See  Nos.  220,  235,  407,  442,  527,  533,  549,  577.) 


DESCRIPTION  OF  ELEMENTS   AND  COMPOUNDS   153 

beds  of  "  rock  salt  "  in  the  earth's  crust.  The  nitrate,  car- 
bonate, sulphate,  silicate,  and  other  salts  of  sodium  are 
found  native,  and  it  is  sometimes  a  constituent  of  plant  and 
animal  organisms. 

Preparation.  —  The  element  was  originally  separated  by  409 
Davy  from  its  hydroxide  by  electrolysis.  Later  its  manu- 
facture was  greatly  cheapened  by  a  process  which  consists 
of  heating  to  a  high  temperature  —  a  white  heat,  in  iron 
cylinders  —  a  mixture  of  sodium  carbonate,  coal  or  charcoal, 
and  chalk  (calcium  carbonate).  The  reaction  is  thus  ex- 
pressed : 

Na,COs  +  2C  =  Na2  +  300. 


The  liberated  sodium  is  separated  by  distillation.  This 
method  was  improved  in  1886  by  Castner,  who  used  sodium 
hydroxide  and  a  mixture  of  iron  and  pitch  (giving,  perhaps, 
a  carbide  of  iron).  By  heating,  is  brought  about  this  re- 
action : 

6NaOH  +  2C  =  2Na  +  6H  +  2Na2C03  ; 


and  the  sodium  is  distilled  as  in  the  first  process.  Still 
later,  since  the  cheapening  of  electricity,  the  older  process 
of  electrolyzing  the  fused  hydroxide  is  coming  into  use. 

Properties.  —  Sodium  is  a  soft,  white,  crystallizable  metal  410 
of  silverlike  luster.  Its  specific  gravity  (solid)  is  0.98,  and 
it  melts  at  96°  and  boils  at  742°.  In  dry  air  it  remains 
untarnished,  but  in  moist  air  it  oxidizes,  and  when  heated 
it  burns  with  a  brilliant  yellow  flame,  forming  both  the 
monoxide,  Na20,  and  the  dioxide,  Na202.  It  combines 
directly  with  fluorine,  chlorine,  bromine,  and  iodine.  It 
decomposes  water  at  ordinary  temperature,  liberating 
hydrogen  and  forming  the  hydroxide,  NaOH,  a  base.  For 
these  reasons  it  is  kept  under  kerosene  or  some  similar 
liquid.  By  heating  in  hydrogen,  a  hydride  is  formed, 
Na2H  (?).  Sodium  combines  with  carbon,  forming  the 
carbide  Na2C2  ,  which  with  water  yields  acetylene,  and  it 
forms  with  nitrogen  the  nitride  Na3N,  which  with  water 


154        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

yields  ammonia.  The  dioxide  does  not  form  salts,  but  it 
readily  yields  one  half  its  oxygen,  and  is  used  somewhat  as 
an  oxidizing  agent. 

Sodium  has  a  considerable  industrial  use  in  obtaining 
other  metals  like  magnesium  and  aluminium  from  their 
chlorides  and  in  processes  involving  the  removal  of  oxygen 
(reduction). 

9a.  Sodium  Chloride,  NaCl 

411  It  has  been  already  stated  that  this  substance  is  formed 
by  direct  action  between  the  elements  and  by  the  action  of 
hydrochloric  acid  on  the  metal  and  on  its  oxide  and  hydrox- 
ide.    But  it  is  the  most  abundant  of  all  the  compounds  of 
sodium,  and  therefore  is  the  available  natural  source  for 
those  manufactured  compounds  which  are  in  commercial 
demand.     It   some  parts   of  the  world  it  is  mined  and 
brought  to  the  surface  like  other  rock.     In  other  places  it 
is  obtained  by  the  evaporation  of  strong  solutions  or  brine. 
In  warm  countries  even  sea  water  is  evaporated  by  expos- 
ure to  the  sun  and  wind  in  order  to  obtain  the  salt  which 
it  contains,  and  in  some  cold  countries  repeated  freezing  is 
resorted  to,  since  removal  of  the  ice,  which  is  relatively 
free  of  salt,  tends  to  concentrate  the  solution.     Salt  is  pro- 
duced in  one  way  or  another  in  many  places,  and  the 
aggregate  is    enormous.      Perhaps    the  best  known  salt 
regions  in  this  country  are  those  of  central  New  York  and 

.  of  Michigan. 

412  Sodium    sulphate,   calcium   sulphate,   and  magnesium 
chloride  often  accompany  common  salt  as  impurities,  and 
the  last  substance   causes  it  to  be   deliquescent.      Pure 
sodium  chloride  does  not  show  this  property  unless  in  air 
saturated  with  moisture.     It  crystallizes  in  cubes  without 
water  of  crystallization,  melts  at   851°  (V.  Meyer),  and 
volatilizes  at  a  slightly  higher  temperature.     One  hundred 
grams  of  water  dissolve  36  grams  of  salt  at  0°,  and  40  grams 
at  100°. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   155     , 

9b.  Sodium  Carbonate,  Na2O03 

This  substance  is  found  in  nature,  but  not  in  sufficient  413 
quantity  to  meet  the  commercial  demand,  and  its  manu- 
facture constitutes  one  of  the  most  important  of  chemical 
industries.  It  is  known  also  as  soda,  soda-ash,  sal-soda,  and 
washing  soda.  Until  1793  its  commercial  source  was  the 
ashes  of  sea  plants.  At  the  time  of  the  revolution  France 
was  cut  off  from  her  supply  of  this  important  article,  and 
the  Government  called  upon  chemists  and  manufacturers  to 
make  public  their  processes  for  making  it  from  common  Salt. 
The  method  invented  by  Leblanc  proved  the  most  success- 
ful, and  is  still  in  use  without  essential  modification.  The 
English  manufacture,  which  has  since  become  very  exten- 
sive, was  started  in  1823  under  the  Leblanc  process. 

The  Leblanc  process,— This,  although  somewhat  compli-  414 
cated  in  the  practical  details,  is  simple  in  the  fundamental 
reactions  which  are  involved.     It  consists  of  three  stages  : 

(1)  The  "  salt-cake  "  process. — This  consists  in  making 
sodium  sulphate  from  the  chloride  by  the  action  of  sul- 
phuric acid.     The  first  reaction  is 

2XaCl  +  H2S04  =  HOI  +  NaHSO,  +  ffaCl. 

When  the  temperature  is  further  raised,  the  second  reac- 
tion takes  place  : 

NaHS04  +  NaCl  =  Na2S04  +  HOI. 

The  hydrochloric  acid  is  condensed  in  water  and  thus 
becomes  a  by-product  in  the  manufacture.  The  salt  cake 
consists  of  sodium  sulphate  to  the  extent  of  96  or  97  per 
cent.  A  considerable  quantity  is  used  in  making  glass. 

(2)  The  "black-ash"  process. — Salt   cake,   100    parts, 
limestone  or  chalk,  100  parts,  and  coal,  50  parts,  are  mixed 
and  heated  in  a  furnace  to  about  1,000°  under  suitable  con- 
ditions.    The  reaction  which  takes  place  is  in  the  main  as 
follows : 


156        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

(a)  Na2S04  +  20  =  Ka2S  +  2C02. 

(b)  :\Ta2S  +  CaC03  =  Ka2C03  +  CaS. 


The  black  ash  appears  as  a  brownish-black  porous  material, 
and  contains  from  37  to  45  per  cent  of  sodium  carbonate, 
about  30  per  cent  of  calcium  sulphide,  CaS,  and  from  5  to 
10  per  cent  of  calcium  oxide,  CaO,  and  many  other  sub- 
stances in  smaller  quantity. 

(3)  Treatment  with  water.  —  The  purpose  of  this  is  to 
dissolve  the  carbonate  and  leave  the  sulphide,  but  undesir- 
able reaction  between  the  substances  is  likely  to  occur, 
especially  if  too  much  water  is  used  or  if  the  temperature 
rises  above  60°.  The  solution  thus  obtained  is  submitted 
to  various  purifications,  is  further  concentrated,  and  finally 
deposits  crystals  of  crude  carbonate.  These,  dried  and 
ignited,  are  "  soda-ash,"  and  by  re-solution,  purification,  and 
crystallization  yield  the  "soda  crystals,"  Na2C03.10H20, 
still  somewhat  impure. 

415  The  Solvay  ammonia  process,  —  Since  1872  large  quanti- 
ties of  sodium  carbonate  have  been  made  by  this  rival 
process.  It  consists  of  saturating  brine  (i.  e.,  a  solution  of 
sodium  chloride)  with  ammonia,  cooling  the  solution,  and 
then  passing  in  carbon  dioxide.  The  reaction  is 

NaCl  +  NH3  +  C02  +  H20  =  NaHCOs  +  NH4C1. 

The  acid  carbonate,  being  less  soluble  than  the  ammonium 
chloride,  is  separated  by  precipitation.  The  reaction  is  not 
complete,  about  one  third  of  the  sodium  chloride  being  lost. 
From  the  acid  carbonate  is  obtained  the  normal  car- 
bonate by  heat  alone  : 

2NaHC03  (heated)  =  Na2C03  +  C02  +  H20. 

The  carbon  dioxide  thus  recovered  is  used  over  again. 
From  the  ammonium  chloride  the  ammonia  is  also  recov- 
ered with  some  loss  : 

2NH4C1  +  Ca(OH)2  =  2NH3  +  CaCl2  +  2H20. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   157 

By  this  process  is  produced  a  soda-ash  of  98  or  99  per 
cent  purity. 

These  two  are  the  chief  commercial  methods  of  produc-  416 
ing  sodium  carbonate,  which  is  consumed  in  great  quan- 
tities, finding  use  in  the  making  of  glass,  of  soap,  of  caus- 
tic soda,  and  for  many  other  industrial  and  domestic  pur- 
poses. 

The  dry  salt  is  hygroscopic  but  not  deliquescent,  melts  417 
at  red  heat,  and  at  higher  temperature  volatilizes.     Its 
solution  has  alkaline  reaction. 

Sodium  acid  carbonate,  NaHC03,  known  also  as  bicar-  418 
bonate  of  soda  and  as  baking  soda,  loses  carbon  dioxide  and 
water  at  a  comparatively  low  temperature,  and  for  this  rea- 
son is  used  as  a  constituent  of  baking  powder. 

9c.  Sodium  Hydroxide,  Caustic  Soda,  NaOH 

This  substance  is  made  from  the  carbonate  or  from  the  419 
crude  material  at  a  certain  stage  of  the  Leblanc  process  by 
removing  the  carbon  dioxide  through  the  action  of  lime, 
Ca(OH)2.  A  dilute  solution  of  the  crude  carbonate  is 
brought  to  boiling  temperature,  and  lime  is  added  with 
constant  stirring.  Calcium  carbonate  is  formed,  and,  with 
the  other  insoluble  material,  is  allowed  to  settle,  and  the 
liquid,  after  various  purifications,  is  concentrated  in  iron 
pots  by  boiling  until  the  temperature  reaches  about  260°, 
when  the  mass  becomes  very  stiff  and  contains  nearly  64 
per  cent  of  sodium  oxide,  Na20.  At  this  stage  air  is  blown 
in  or  nitrate  is  added,  in  order  to  oxidize  the  remaining 
sulphide.  The  mass  is  kept  in  a  fused  state  for  eight  or 
twelve  hours,  by  which  impurities  of  iron,  aluminium,  and 
silicon  oxides  settle  to  the  bottom.  The  clear  liquid  is 
then  ladled  off  into  iron  drums  or  other  suitable  vessels, 
in  which  it  solidifies  on  cooling.  In  this  form  it  appears 
in  commerce.  It  is  also  produced  in  granular  condition. 
(Compare  No.  546.)  The  commercial  article  may  contain 
as  much  as  95  or  96  per  cent  of  the  hydroxide,  and  as 


158       ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

impurities  some  carbonate,  sulphate,  chloride,  silicate,  and 
aluminate.  It  is  used  extensively  in  soap-making,  paper- 
making,  bleaching,  in  the  manufacture  of  dyestuffs  and  of 
wood  pulp,  in  refining  oil,  and  in  many  other  operations. 
(Lunge,  in  Thorpe's  Dictionary  of  Applied  Chemistry.) 

420  The  purer  material  for  chemical  purposes  often  appears 
cast  in  sticks.     It  is  a  white  crystalline  solid  which  absorbs 
water  and   carbon   dioxide   from  the  air.     It  melts  and 
volatilizes.     It  is  very  soluble  in  water  (about  2  parts  to  1 
of  water),  dissolving  with  evolution  of  heat.     A  crystal- 
lized hydrate,  2NaOH-7H20,  is  obtainable,  which  dissolves 
with  absorption  of  heat.     The  hydroxide  is  a  powerful 
base,  and  its  solution  is  much  used  in  the  laboratory. 

421  Of  the  other  salts  of  sodium,  the  sulphate  occurs  natu- 
rally, and  its  manufacture  has  already  been  described.     It 
is  known  sometimes  as  Glauber's  salt.     The  nitrate,  known 
as  Chili  saltpeter,  is  found  abundantly,  and  is  valuable  as  a 
source  of  nitric  acid.     It  is  also  converted  into  potassium 
nitrate,  which  is  used  extensively  in  making  gunpowder. 
The  borate — i.  e.,  borax — has  been  referred  to  in  connec- 
tion with  boric  acid. 

D.   GENERAL  SURVEY 

422  Nine  elements  have  now  been  considered  descriptively, 
and  there  will  be  gain  in  taking  a  general  view  of  their 
properties  for  the  purpose  of  comparison,  first  with  refer- 
ence to  some  physical  properties.     As  to  condition  at  ordi- 
nary temperature,  it  is  to  be  noted  that  the  first  one  is 
gaseous ;  then  follow  four  which  are  solid ;  the  next  three 
are  gaseous,  and  the  ninth  is  solid.     Closer  examination  as 
to  this  matter,  by  comparison  of  melting  or  boiling  points 
(see  Table  VI,  No.  433),  shows  that  among  the  solids  the 
melting  point   tends   to   rise   with   increasing   combining 
weight  for  the  four— lithium,  glucinum,  boron,  and  carbon ; 
and  then  to  drop  to  a  low  value  for  the  next  one— namely, 
sodium. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   159 

As  to  combining  volume — that  is,  the  volume  in  cubic  423 
centimeters  occupied  by  the  combining  weight  measured 
in  grams— it  should  be  recalled  that  these  volumes  are 
approximately  equal  for  the  elements  in  gaseous  condition 
(Law  of  Gay-Lussac);  for  solids  and  liquids  the  case  is 
different.  In  column  III  are  given  these  combining  vol- 
umes. They  are  equal  to  the  combining  weight  divided 
by  the  specific  gravity  of  the  solid  or  liquid.  It  is  to  be 
observed  that  they  go  decreasingly  from  lithium  through 
carbon,  and  then  increasingly  to  sodium. 

Comparison  as  to  the  chemical  relations  is  next  made,  424 
and  of  these,  first  as  to  the  fact  of  combination  with  other 
elements,  forming  binary  compounds — i.  e.,  compounds  of 
two  elements  only.  It  is  interesting  to  note  that  all  the 
elements  so  far  considered  exist  in  binary  compounds 
with  hydrogen  and  with  chlorine,  and  all  except  fluorine 
with  oxygen.  This  leads  to  the  question :  May  each  ele- 
ment combine  with  every  other  one?  Now,  the  metals, 
like  lithium,  glucinum,  and  sodium,  as  a  general  rule,  mix 
with  each  other  in  the  liquid  condition  and  form  what  are 
called  alloys,  but  there  is  more  or  less  doubt  whether  these  425 
should  be  reckoned  as  chemical  compounds,  or  as  phys- 
ical mixtures.  Furthermore,  the  existence  of  borides  of 
lithium,  of  glucinum,  and  of  sodium  seems  unproved, 
although  not  improbable.  With  these  exceptions,  it  may 
be  affirmed  that  each  element  is  known  to  exist  in  binary 
combination  with  every  other  one,  so  far  as  concerns  the 
first  nine. 

As  to  readiness  of  combination — that  is,  the  readiness  426 
to  enter  directly  into  combination  with  other  elements — 
hydrogen  combines  directly  with  lithium,  but  only  on 
heating,  and  the  heating  must  be  continued,  or  the  reac- 
tion ceases ;  similarly  with  glucinum.  Direct  union  be- 
tween hydrogen  and  boron  seems  not  to  have  been  observed. 
With  hydrogen  and  carbon,  the  union  takes  place  only  un- 
der the  influence  of  the  electric  arc ;  similarly  with  nitro- 


160        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

gen.  With  hydrogen  and  oxygen,  direct  union  takes  place 
on  elevation  of  temperature,  and  the  reaction  is  continuous, 
while  explosive  union  with  fluorine  takes  place  at  ordinary 
and  even  very  low  temperatures.  With  sodium,  direct  com- 
bination is  effected  as  in  the  case  of  lithium. 

427  Oxidation  in  the  case  of  hydrogen  is  already  consid- 
ered; with  lithium  it  takes  place  at  slight  elevation  of 
temperature  ;  with  glucinum,  boron,  and  carbon  at  higher 
temperature;    with   nitrogen   only   under   strong   electric 
influence ;    similarly   with  oxygen    (formation   of   ozone) ; 
with  fluorine  not  at  all ;  and  with  sodium  about  the  same 

428  as  with  lithium.     Indeed,  with  the  exception  of  sodium,  it 
would  seem  that  the  elements  so  far  considered  enter  into 
combination  with  each  other  the  more  readily  as  they  are 
further  removed  from  each  other  in  the  list. 

429  As  to  energy  of  combination,  comparison  may  be  made 
by  noting  the  quantities  of  heat  liberated  in  combining 
with   oxygen,   and  also   with   chlorine.     These  values,   so 
far  as  determined,  are  given  in  columns  VI  and  VIII.     In 
both  instances  it  is  seen  that  the  values  tend  to  increase 
to  a  maximum  and  then  decrease,  and  that  the  change  is 
very  marked  in  passing  from  fluorine  to  sodium. 

430  As  to  capacity  of  combination :  By  comparing  the  for- 
mulas of  the  chlorine  compounds  in  order  (column  VII),  it 
is  seen  that  the  coefficient  of  the  chlorine  symbol,  begin- 
ning with  one,  increases  to  four  for  carbon,  then  decreases 
to  one  for  sodium.    The  capacity  of  combination  thus  illus- 
trated is  named  valence.     It  is  an  important  phenomenon, 
and  calls  for  some  further  consideration  (No.  434). 

431  As  to  base-forming  and  acid-forming  oxides :  For  con- 
venience the  basic  function  may  be  represented  by  the  plus 
sign  and  the  acidic  by  the  minus  sign.     The  facts  are  thus 
tabulated  in  column  V :    Lithium  oxide  acts  only  as  base ; 
the  oxide  of  glucinum  acts  primarily  as  base,  but  in  the 
glucinates  as  acid ;  that  of  boron  is  primarily  acid,  but  in 
the  compound,  BP04,  seems  to  act  as  base ;  those  of  car- 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    161 


bon  and  nitrogen  show  no  basic  function ;  that  of  sodium 
is  basic  only.  The  disappearance  of  the  basic  function, 
the  appearance  of  the  acidic,  and  the  reappearance  of  the 
former  with  sodium  are  very  remarkable. 

It  will  be  recalled  that  this  descriptive  work  has  been  432 
introduced  under  the  general  topic,  "  The  relation  between 
the  properties  in  general  of  the  elements  and  their  com- 
'bining  weights."  But  up  to  this  point  there  has  been  no 
suggestion  as  to  the  nature  of  the  relation.  The  clew  to 
this  will  perhaps  be  seen  in  this  general  survey,  but  it  will 
not  be  formulated  until  later  in  the  course.  It  is  recom- 
mended that  the  student  in  the  meantime  bear  the  ques- 
tion in  mind,  to  see  if  he  can  not,  by  following  the  clew 
already  given,  trace  the  development  of  the  relation  in  the 
continuation  of  descriptive  facts  soon  to  be  presented. 


TABLE  VI 


H... 
Li  .. 
Gl  .. 
B... 
C... 
N.... 
0.... 
F... 
Na.. 

IL 

Melting  points. 
Boiling  points. 

ill. 

Combining 

volumes. 

IV. 
Oxides. 

v. 

Base 
and 
acid. 

v 

+ 
+  - 
-4 

? 

9 
+ 

VI. 

Formation  heat  of 
oxides. 

VII. 

Chlorides. 

VIII. 

Formation 
heat  of 
chlorides. 

B.  P.  -238° 
M.  P.  180° 
M.  P.  1,230° 
(Sublimes)  3,600°? 
(Sublimes)  3.600°? 
B.  P.  -194° 
B.  P.  -183° 
B.  P.  -187° 
M.  P.  96° 

(Liquid)  14 
11.8 
4.9 
4.4 
(T)iamond)3.4 

9 

(Liquid)  14.  3 
(Liquid)  16.6 
23.2 

H20 

Li20 
GIG 
B208 
C02 
NaO, 

°3? 
Na2O 

Calories. 
(Liquid)  68,400 
141,200 
? 
317,200 
97,000 
-23,000 
-32,400 

9 

100,400 

HC1 
LiCl 
GlCla 
BC13 

ecu 

NC13 
OC12 

NaCl 

Calorie.. 
22,000 
93,800 

104,000 
21,000 
-38,100 
-17,800 

9 

97,600 

433 


E.  VALENCE 

The  valence  of  an  element  is  by  definition  its  capacity  434 
of  combination,  as  measured  by  the  multiple  of  the  com- 
bining weight  of  hydrogen  which  enters  into  combination 
with  the  combining  weight  of  the  element  in  question.  It 
is  seen,  therefore,  in  the  coefficients  of  H  in  the  formulas  of 
the  hydrides— for  example,  HF,  H20,  H3N,  and  H4C.  Hy- 
drogen being  made  the  unit,  it  is  assumed  that  the  capacity 
of  combination  of  one  gram  of  this  element  is  the  same 


162        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

in  all  compounds.  The  four  hydrides  just  mentioned  are 
gaseous,  and  their  formulas  are  well  established  by  the 
law  of  Gay-Lussac  concerning  vapor  densities ;  but  the  hy- 
drides of  lithium  and  glucinum  are  not  gaseous,  and  the 
composition  of  boron  hydride  is  not  yet  well  established. 
Of  many  other  elements  also  it  is  true  that  they  do  not 
form  hydrides,  or 'that  the  composition  and  vapor  density 

435  of  the  same  are  not  determined.     However,  most  such  ele- 
ments do  form  chlorides,  and  chlorine  and  hydrogen  must 
have  the  same  capacity  of  combination,  since  their  com- 
pound has   the   formula   HC1  established  by  quantitative 
relation  both  in  weight  and  in  volume,  and  by  the  specific 
gravity  of   the  gaseous  compound.      Chlorine,  therefore, 
may  be  taken  as  the  measure  of  valence  when  hydrogen 
is  not  available.     The  series  of  chlorides  is  exhibited  in 
column  VII. 

436  Better  to  appreciate  the  basis  of  valence,  let  the  argu- 
ment be  recalled  which  led  to  the  choice  of  certain  mul- 
tiples of  the  equivalent  weights  to  be  used  as  combining 
weights  of  the  elements  (see  Nos.  136,  137,  150,  and  151, 
Part  I).     This  choice  was  determined  by  relations  of  spe- 
cific gravity,  of  specific  heat,  of  depression  of  freezing  point 
and  elevation  of  boiling  temperature  in  solutions,  besides 
others  which  were  not  specified.    In  addition,  it  was  stated 
that  the  choice  was  greatly  strengthened  by  the  relation  of 
the  elements  as  to  their  properties  in  general.     The  force 

.of  this  relationship  may  now  be  seen.  Carbon  was  the 
element  then  used  for  illustration,  and  the  choice  for 
combining  weight  of  the  multiple  by  four  of  its  equivalent 
weight  was  in  question,  since  the  specific  gravity  of  gaseous 
carbon  is  unknown.  It  is  now  evident  that  were  any  other 
multiple  chosen,  the  position  of  carbon  in  the  series  of  ele- 
ments would  be  changed,  and  the  remarkable  progression 
of  properties  brought  out  in  this  general  survey  would 
disappear.  From  this  point  of  view  it  is  seen  that  the 
measure  of  valence  is  found  in  the  factor  by  which  the 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   163 

equivalent  weight  is  multiplied  to  produce  .the  combining 
weight. 

Clearly,  then,  the  .valence  of  elements  is  best  determined  437 
in  their  binary  compounds  with  hydrogen  or  with  chlorine. 
Those  whose  combining  capacity  is  equal  to  that  of  hydro- 
gen or  chlorine  are  called  monads,  and  are  said  to  be  univa- 
lent ;  those  which  have  twice  the  capacity  of  hydrogen  or 
chlorine  are  called  diads,  and  said  to  be  bivalent ;  corre- 
spondingly, those  which  have  ''three,  four,  five,  six,  and 
seven  times  the  capacity  of  hydrogen  are  named  respect- 
ively triads,  tetrads,  pentads,  hexads,  and  heptads.  The 
adjectives  are  trivalent,  quadrivalent,  quinquivalent,  sexiva- 
lent,  and  septivalent. 

Statement  I. — The  valence  of  a  given  element  may  vary  438 
in  combination  with  the  same  substance ;  for  example,  in 
hydrogen  dioxide,  H202,  the  valence  of  oxygen  appears  to 
be  one  half  that  of  the  same  element  in  water,  H20  ;  so  also 
the  valence  either  of  carbon  or  of  oxygen  must  vary  in  the 
compounds,  CO  and  C02  ;  and  the  valence  of  nitrogen  or  of 
oxygen  must  vary  in  the  compounds,  N20  and  NO.  In- 
deed, every  instance  of  multiple  proportions  must  indicate 
apparent  variation  in  valence. 

Statement  II. — The  valence  of  a  given  element  may  vary  439 
according  to  the  substance  in  combination  with  it.  Thus 
if  oxygen  is  a  diad,  then  nitrogen  in  the  substance,  NO, 
must  act  as  a  diad  ;  but  in  ammonia,  H3N,  it  is  certainly  a 
triad  ;  in  ammonium  chloride,  NH4C1,  if  it  be  granted  that 
four  fifths  of  the  capacity  of  nitrogen  is  taken  with  hydro- 
gen and  one  fifth  with  chlorine,  the  nitrogen  must  be  act- 
ing as  a  pentad. 

Statement  III. — Valence  must  influence  the  phenome-  440 
non  of  substitution  as  well  as  that  of  combination.  Thus 
lithium  and  sodium  are  univalent  in  their  chlorides,  LiCl 
and  NaCl.  They  must  therefore  act  as  monads  in  the  re- 
placement of  hydrogen  from  hydrochloric  acid  and  other 
acids.  This  is  seen  again  'in  the  nitrates,  LiK03  and  Na- 
12 


164        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

N03,  in  the  carbonates,  Li2C03  and  Na2C03,  and  in  the 
acid  carbonates,  LiHC03  and  NaHC03.  Concerning  mag- 
nesium and  zinc,  let  it  be  recalled  that  24  grams  of  one  and 
65  grams  of  the  other  replace  2  grams  of  hydrogen  ;  they 
are  therefore  diads,  and  their  chlorides  are  MgCl2and  ZnCl2, 
their  nitrates  Mg(N03)2  and  Zn(N03)2,  and  their  carbonates 
MgC03  and  ZnC03.  In  other  words,  the  capacity  of  combi- 
nation has  the  same  value  as  the  capacity  of  substitution. 
(Compare  Law  IY,  Equivalent  Proportions.) 
441  Statement  IV. — The  valence  of  a  compound  is  regarded 
as  dependent  on  the  valence  of  its  constituents.  If  the 
maximum  valence  of  these  is  not  exhausted,  then  the  com- 
pound may  add  to  itself  some  substance,  or  combine  addi- 
tively,  as  it  is  expressed.  Thus  the  capacity  of  14  grams  of 
nitrogen  is  not  exhausted  in  ammonia,  NH3 ,  since  the  lat- 
ter combines  with  hydrochloric  acid  additively,  forming 
ammonium  chloride,  XH4C1,  in  which  the  capacity  of  nitro- 
gen is  exhausted.  So  also  nitric  oxide,  NO,  takes  on  oxy- 
gen and  becomes  the  peroxide,  N02 ;  and  CO  becomes  by 
combustion  C02.  The  same  is  seen  in  compounds  of  greater 
complexity,  for  sodium  nitrite,  NaN02 ,  becomes  by  oxida- 
tion the  nitrate,  NaN03.  Those  substances  capable  of  addi- 
tive reaction,  and  therefore  possessing  a  residual  valence, 
are  called  unsaturated,  the  others  saturated. 

441/a  Statement  V. — The  phenomena  of  oxidation  and  reduc- 
tion (see  Nos.  47/4,  48,  and  208/j,  Part  II),  in  which  one 
substance  takes  the  oxygen  that  another  substance  gives 
up,  involve,  as  is  evident,  a  change  in  valence.  Thus  when 
ferrous  oxide,  FeO,  is  changed  to  ferric  oxide,  Fe203,  or 
when  ferrous  salts  are  changed  to  ferric  salts  by  the  oxygen 
which  nitric  acid  yields,  the  active  valence  of  the  iron  is 
increased  from  two  to  three  and  that  of  the  nitrogen  is 
reduced  from  five  to  two,  for  that  of  the  oxygen  is  reckoned 
as  constant.  The  terms  oxidation  and  reduction  are  some- 
times applied  to  similar  changes  in  valence  when  the  ele- 
ment oxygen  is  not  at  all  involved.  Thus  the  change  of 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   165 

mercuric  to  mercurous  iodide  by  reaction  with  added  mer- 
cury may  be  spoken  of  as  reduction ;  and  the  change  of 
mercurous  to  mercuric  iodide  by  reaction  with  added  iodine 
is  sometimes  designated  as  oxidation,  although  this  seems 
an  unfortunate  extension  of  meaning. 

REVIEW  PROBLEMS 

1.  How  many  grams  of  hydrogen  should  be  liberated  by  the  action   441/1 
of  10  grams  of  pure  sodium  on  water  1    What  is  the  volume  of  this 

mass  at  0°  and  760  millimeters  (one  liter  of  hydrogen  weighs  0.0899  of 
a  gram  at  0°  and  760  millimeters)  f 

2.  Suppose  that  10  grams  of  pure  carbon  are  burned  in  oxygen,  how 
much  does  the  product  of  combustion  weigh  ?    What  is  its  volume  (one 
liter  =  1.98  grams)  f    What  is  the  volume  of  the  oxygen  contained  in  it  I 

3.  What  is  the  specific  gravity  of  methane  (H  =  1)  f    What  is  the 
volume  of  the  combustion  products  from  one. liter  of  methane?    What 
is  their  total  mass  1 

4.  Suppose  that  one  liter  of  water  vapor  is  passed  over  hot  carbon 
and  completely  decomposed,  what  is  the  volume  of  the  products  taken 
under  the  same  conditions  of  temperature  and  pressure  as  the  water 
vapor  f 

5.  What  is  the  specific  gravity  of  ammonia  gas  (H  =  1)  1    Suppose 
one  liter  of  dry  ammonia  gas  is  to  be  obtained  from  ammonium  chlo- 
ride, how  may  it  be  done,  and  how  much  of  the  latter  substance  is  theo- 
retically needed  ? 

6.  What  is  the  ratio  between  the  masses  of  dry  ammonia  and  pure 
sodium  hydroxide,  which  in  water  solution  neutralize  equal  quantities 
of  hydrochloric  acid  I 

7.  How  much  dry  sodium  carbonate  is  needed  to  make  10  grams 
of  sodium  nitrate?     To  make  10  grams  of  sodium  chloride? 

8.  Assume  that  one  gram  of  diamond  is  completely  burned,  and  the 
product  of  combustion  completely  absorbed  by  sodium  hydroxide,  how 
much  carbonate  is  thus  produced  ? 

9.  Assume  that  carbon  dioxide  is  liberated  from  the  carbonate  thus 
produced  (problem  8)  and  completely  reduced  to  carbon  by  hot  magne- 
sium, how  much  magnesium  oxide  is  thus  produced  f 

10.  As  between  26  grams  of  acetylene  on  one  hand,  and  on  the 
other  24  grams  of  carbon  and  2  grams  of  hydrogen  which  the  former 
contain,  which  gives  out  more  heat  in  burning  ?    (See  No.  57,  Part  I.) 

As  between  methane  and  acetylene,  at  the  same  price  per  cubic  foot, 
which  is  the  more  effective  fuel,  assuming  complete  combustion  in  both 


166        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

cases  f    (See  No.  57.    The  formation  heat  of  methane  is  21,800  calories.) 
What  is  the  ratio  of  efficiency  ? 

11.  Assume  that  "  natural  gas  "  is  pure  methane,  that  pure  calcium 
carbide  is  obtainable,  that  one  cubic  foot  of  acetylene  weighs  1.17 
ounces,  and  that  the  cost  of  water  is  zero — at  what  price  per  pound 
for  the  calcium  carbide  would  acetylene  be  as  cheap  for  fuel  as  "  natu- 
ral gas  "  at  fifty  cents  per  thousand  cubic  feet  f 


10.  MAGNESIUM 

Mg.-24.10 

442  History. — Magnesia  was  distinguished  from  lime  in  1755,  but  Davy 
was  the  first  to  separate  the  metallic  element. 

443  Natural  occurrence. — It  is  not  found  free,  but  is  abundant 
as  a  constituent.     The   mineral   dolomite,  which  is   very 
abundant,  is  the  carbonate  of  magnesium  and   calcium. 
Magnesite  is  the  carbonate.     Asbestos,  talc,  or  soapstone, 
and  meerschaum  contain  it  as  a  silicate.     The  sulphate  is 
known  as  Epsom  salt  and  is  found  in  mineral  waters,  as  is 
also  the  chloride.     It  occurs  in  small  quantity  in  the  plant 
and  animal  organism,  and  the  spectroscope  shows  it  pres- 
ent in  the  sun. 

444  Preparation. — It  is  obtained  from  the  fused  chloride  by 
electrolysis  and  by  the  action  of  sodium  : 

MgClj  +  fcNa  =  Mg  +  2NaCl. 

It  is  purified  by  distillation  in  hydrogen  or  coal  gas. 

445  Properties. — It  is  a  metal  of  a  clear,  white  color.     It  is 
malleable,  and  when  heated  it  is  ductile — that  is,  it  can  be 
hammered  or  rolled  into  thin  sheets  and  drawn  into  wire. 
Its  specific  gravity  is  only  1.75.     It  melts  at  red  heat,  700° 
to  800°,  and  boils  at  about  1,000°.     It  does  not  oxidize  in 
dry  air  and  only  superficially  in  moist  air.     Heated  in  air, 
it  burns  with  an  intensely  brilliant  light,  which  fact  is 
made  use  of  in   signaling,   in  pyrotechnics,  and  in  pho- 
tography.    The  oxide,  MgO,  is  produced  in  burning,  and, 
if  the  oxygen  be  insufficient,  considerable  nitride,  Mg3N2j 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   16? 

is  also  produced  by  direct  union  with  the  nitrogen.  It 
combines  when  heated  with  hydrogen  (MgH  ?),*  with 
boron,  carbon  (MgC2),  nitrogen,  oxygen,  fluorine,  chlorine 
(Mg012),  bromine,  iodine,  silicon,  phosphorus,  and  sulphur. 
It  slowly  decomposes  boiling  water  and  is  quickly  acted 
upon  by  dilute  acids.  Its  energetic  combination  with  oxy- 
gen makes  it  a  powerful  reducing  agent. 

Its  sole  oxide,  MgO,  known  also  as  magnesia,  appears  446 
generally  as  a  fine  white  powder,  almost  insoluble  in  water, 
but  soluble  by  dilute  acids  with  the  formation  of  salts.  It 
melts  and  crystallizes  only  at  extremely  high  temperature, 
but  does  not  decompose ;  it  is  therefore  the  most  service- 
able material  for  the  construction  of  electric  furnaces  and 
for  similar  uses.  Its  boiling  point  is  not  far  above  its  melt- 
ing point  (Moissan).  With  water  it  forms  the  hydroxide, 
Mg02H2,  which  is  only  sufficiently  soluble  in  water  to  give 
alkaline  reaction  with  litmus,  and  which  dissolves  in  acids, 
but  not  in  potassium  or  sodium  hydroxide. 

Of  the  salts  of  magnesium  the  following  are  the  most  447 
important  commercially  :  The  chloride,  Mg012 ;  carbonate, 
MgC03;  nitrate,  Mg(N03)2;  and  sulphate,  MgS04. 

11.  ALUMINIUM 

A1.-26.9 

History. — Alum,  a  salt  of  aluminium,  was  known  to  the  alchemists,  448 
Geber  and  Paracelsus.  Much  later,  in  1754,  it  was  learned  that  the 
earthy  base  of  alum,  which  was  named  alumina,  is  unlike  that  of  lime 
and  the  same  as  that  of  clay.  But  it  was  not  until  1827  that  the  element 
was  obtained  from  its  oxide,  alumina.  Its  name,  therefore,  comes  from 
its  salt,  alum.  (The  spelling,  aluminum,  is  in  equally  good  usage.) 

Natural  occurrence. — It  has  not  been  found  free  ;  but  as  449 
a  constituent,  next  to  oxygen  and  silicon,  it  is  the  most 
abundant  and  most  generally  distributed  of  the  elements 
in  the  earth's  crust.     The  oxide,  A1203,  constitutes  corun- 

*  Winkler,  Ber.  Chem.  Ges.,  24  (1891). 


168        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

dum,  and  when  crystallized  the  ruby  (red)  and  the  sapphire 
(blue).  Bauxite  is  the  hydrated  oxide,  A1203-2H20,  with 
iron  oxide.  As  silicate,  alumina  is  present  in  very  many 
minerals — e.  g.,  feldspar,  granite,  garnet,  mica,  slate,  soap- 
stone,  and  clay.  Cryolite  is  a  fluoride,  A12F6  •  6NaF ;  tur- 
quoise, a  phosphate.  It  is  found  in  fertile  soils  and  to  some 
extent  is  taken  up  by  plants  (Berthelot).  By  the  spectro- 
scope its  presence  in  the  sun  is  revealed. 

450  Preparation. — Wohler  obtained  it  by  reaction  between 
dry  aluminium  chloride  and  potassium;  Bunsen  and  De- 
ville  in  1854  by  the  electrolysis  of  the  fused  chloride  ;  and 
Deville  about  the  same  time  by  the  action  of  sodium  on 
the  fused  double  chloride  of  aluminium  and  sodium.     In 
consequence  mainly  of  the  latter's  work  it  was  prepared  in 
quantity  promising  a  commercial  supply,  and  his  method 
remained  for  thirty  years  practically  the  only  one  in  use. 
Before  considering  more  fully  the  manufacture  of  the  metal, 
it  is  best  to  study  its  properties  and  some  of  its  compounds. 

451  Properties. — It  is  a  white,  lustrous  metal  with  a  specific 
gravity  of  2.58  (cast)  or  2.7  (hammered),  which  is  remark- 
ably low  as  compared  with  that  of  zinc  7.1,  tin  7.3,  iron  7.8, 
copper  8.9,  silver  10.5,  and  lead  11.4.    It  melts  at  about  660° 
(Holman,  1896),  and  volatilizes  only  at  the  extremely  high 
temperature  of  the  electric  furnace.     In  compact  condition 
it  gives  out  a  peculiar  sound  when  struck.     Like  other 
metals,  it  is  a  good  conductor  of  heat  and  electricity.     It 

.  may  be  worked,  like  gold  and  silver,  into  very  thin  leaf  of 
0.000638  millimeters  (one  forty-thousandth  of  an  inch)  in 
thickness,  and  it  may  be  drawn  into  very  fine  wire.  It  has 
great  tensile  strength  as  compared  with  other  metals,  and 
this  and  its  low  specific  gravity  make  a  combination  of 
properties  very  valuable  in  mechanical  applications. 

452  Aluminium  does  not  easily  combine  with  oxygen.     It 
tarnishes  very  slightly  in  air,  and  even  when  melted  oxi- 
dizes only  superficially,  but  at  white  heat  it  burns  bril- 
liantly, forming  the  oxide,-  A1203.     If  in  the  form  of  very 


FRIEDRICH   WOHLER 

B.  Germany,  1800.     D.  1882. 

(See  Nos.  178,  216,  450.) 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   169 

thin  leaf,  it  burns  more  readily.  In  compact  form  the 
metal  does  not  appreciably  decompose  water  even  at  red 
heat.  But  this,  like  the  difficulty  of  direct  oxidation,  is 
probably  due  to  the  formation  of  a  film  of  oxide  which  pro- 
tects the  metal  from  further  action.  If  this  protection  is 
reduced  or  removed,  the  reaction  goes  on.  Thus  the  thin 
leaf  slowly  decomposes  water  at  100,°  with  the  liberation  of 
hydrogen.  Likewise,  if  a  soluble  salt  of  aluminium  be 
present  in  the  water,  the  action  goes  on,  for  the  protecting 
film  is  dissolved  by  the  salt.  If  the  metal  is  dissolved  in 
mercury,  or  if  the  clean  surface  is  simply  rubbed  with  mer- 
cury, it  decomposes  water  at  ordinary  temperature.  With  453 
hydrochloric  acid  the  pure  metal  reacts  readily,  form- 
ing the  soluble  chloride  and  hydrogen;  but  with  dilute 
sulphuric  acid  and  with  nitric  acid  the  action  in  ordinary 
circumstances  is  inappreciable ;  but  it  goes  on  progressively 
if  the  metal  is  finely  divided,  or  if  the  pressure  of  the 
atmosphere  on  the  surface  of  the  liquid  is  removed,  so  that 
the  liberated  hydrogen  is  free  to  escape  from  the  surface  of 
the  metal.  It  dissolves  readily  in  the  presence  of  sodium 
chloride  and  other  chlorides  with  the  addition  of  a  little 
free  acid,  such  as  acetic.  In  solution  of  sodium  or  potas- 
sium hydroxide  it  dissolves  easily,  liberating  hydrogen  and 
forming  the  aluminate  in  which  its  oxide  acts  as  acid  to 
the  alkali  base  (Na2OAl203,  and  K2OA1203).  In  ammo- 
nium hydroxide  the  action  is  slower. 

The  metal  combines  directly  with  fluorine,  chlorine,  454 
bromine,  and  iodine,  forming  A12X6  or  A1X3;  also  with 
boron,  carbon,  (C3A14),  nitrogen,  (A1N),  silicon,  and  sul- 
phur, (A12S3 ).  A  compound  with  phosphorus,  A13PB,  has 
been  obtained.  [L.  Frank  and  Eossel,  Ber.  Chem.  Ges.,  27 
(1894).] 

The  commercial  metal. — The  presence  of  impurities  changes  consid-   455 
ably  the  properties  of  the  metal,  both  physical  and  chemical,  and  there- 
fore the  descriptions  by  different  observers  vary  greatly  according  to 
the  sample  examined.     The  usual  impurities  of  the  commercial  metal 


ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

are  iron,  silicon,  carbon,  nitrogen,  and  sodium.  Their  presence  prob- 
ably tends  to  make  the  impure  metal  harder,  and  of  higher  melting 
point,  to  reduce  the  tenacity,  malleability,  and  ductility,  and  to  increase 
the  readiness  to  react  chemically. 

456  Alloys. — This  is  the  name  given  to  the  compounds  or  mixtures  of 
metals  with  metals.  In  many  cases  fused  metals  may  be  mixed  in  all 
proportions,  and  in  some  instances  there  seems  to  be  real  chemical 

.  union,  as  shown  by  the  evolution  of  heat  and  the  formation  of  crystal- 
lizable  compounds  of  definite  composition.  Still,  the  true  nature  of 
alloys  is  not  at  all  well  understood. 

45  7  Aluminium  forms  alloys  with  readiness,  and  they  have 
special  interest.  Although  a  small  percentage  of  iron  in 
aluminium  deteriorates  it,  on  the  other  hand  a  small  per- 
centage of  aluminium  in  iron  and  steel  is  advantageous. 
Aluminium  forms  alloys  with  copper  in  all  proportions. 
The  one  containing  ten  per  cent  of  aluminium  is  known  as 
"  aluminium  bronze."  It  rivals  the  best  steel  in  tenacity, 
is  very  hard,  casts  well,  may  be  highly  polished,  and  resists 
corrosion  well.  These  properties  adapt  it  to  many  useful 
applications. 

458  The  oxide,  alumina. — The  single  oxide  of  aluminium  has 
the  composition  A1203 .  Its  natural  occurrence  as  corun- 
dum, ruby,  and  sapphire  has  already  been  mentioned.  Emery 
is  an  impure  form  containing  iron.  Alumina  is  made  by 
burning  the  metal,  also  by  drying  the  hydroxide.  Artificial 
rubies  and  sapphires  are  made  by  dissolving  alumina  in 
fused  barium  fluoride  and  allowing  it  to  crystallize.  A 
.  trace  of  chromate  is  added  to  make  the  ruby,  or  of  cobalt 
oxide  to  make  the  sapphire.  The  crystals  thus  obtained 
have  all  the  properties  of  the  natural  crystals.  They  are 
next  to  the  diamond  in  hardness.  The  oxide  in  the  amor- 
phous condition  is  a  white  powder.  It  melts  and  volatilizes 
in  the  heat  of  the  electric  arc.  It  is  insoluble  in  water,  but 
dissolves  in  acids  and  in  sodium  and  potassium  hydroxides. 
By  strong  heating  its  density  is  increased,  and  it  is  less 
readily  acted  upon  chemically.  It  acts  both  as  a  base-form- 
ing and  as  an  acid-forming  oxide. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS   171 

The  hydroxide,  A1203-3H20  or  A1206H6. — This  appears  as  459 
a  white  gelatinous  precipitate  when  a  solution  of  a  hydrox- 
ide, as  that  of  sodium,  or  potassium,  or  barium,  is  added  to 
a  solution  of  an  aluminium  salt : 

A13016  +  6tf  aOH  =  A1206H6  +  GXaCl. 

It  is  insoluble  in  water,  although  a  peculiar,  allotropic 
form  is  soluble,  but  it  dissolves  in  acids,  in  sodium  hydrox- 
ide and  potassium  hydroxide,  and  in  the  solution  of  a  nor- 
mal aluminium  salt,  in  the  last  case  forming  a  basic  salt. 
It  dissolves  but  slightly  in  ammonium  hydroxide.  Besides 
the  tri-hydrate,  the  di-hydrate,  A1203-2H20,  and  the  mono- 
hydrate  A1203-H20.  occur  as  natural  minerals. 

Uses.— The  hydroxide  has  a  peculiar  property  of  uniting,  either  460 
chemically  or  mechanically,  with  many  dyestuffs.  If  the  solution  of 
a  dye  is  added  to  the  solution  of  an  aluminium  salt,  or  of  an  aluminate, 
and  the  hydroxide  is  then  precipitated,  it  carries  in  many  instances 
the  color  stuff  into  the  precipitate.  This  mixture  is  called  technically 
a  "  lake."  By  means  of  this  property,  dyes  are  "  fixed  "  in  textile  fibers 
which  otherwise  would  not  retain  the  color.  When  the  hydroxide  is 
deposited  in  or  upon  the  fiber  and  there  retains  the  dye,  it  is  called  a 
"  mordant."  The  aluminium  compounds  find  extensive  use  as  mordants. 

Aluminium  salts, — The  chloride,  when  anhydrous,  is  vola-  461 
tile  without  decomposition,  and  its  vapor  density  at  low 
temperature  indicates  the  formula  A12C16,  and  at  high 
temperature  A1C13.  It  is  soluble  in  water,  but  can  not  be 
recovered  from  solution  by  evaporation,  as  it  loses  acid  and 
becomes  the  hydroxide. 

The  sulphate,  A12(S04)3,  is  the  most  common  of  the 
salts.  With  the  alkali  sulphates,  it  forms  double  salts 
which  crystallize  readily.  They  are  called  the  alums,  com-  461/1 
mon  alum  being  K2S04-  A12(S04)3-24H20.  The  same  term 
has  come  to  be  applied  to  the  similar  double  sulphates  with 
other  bases  than  aluminium — e.  g.,  iron  and  chromium. 
Common  or  potash  alum  is  found  as  a  natural  mineral  to 
some  extent,  and  is  manufactured  in  large  quantity,  being 
used  not  only  as  a  mordant,  but  in  the  making  of  leather, 


172        ELEMENTARY  PEINCIPLES  OF  CHEMISTRY 

of  paper,  of  fire-proof  material,  etc.  Its  manufacture  and 
use  as  a  mordant  are  of  great  antiquity. 

The  salts  with  silicic  acid — i.  e.,  the  silicates — occur  in 
great  variety  as  natural  minerals.  The  carbonate  and  the 
sulphide  are  not  formed  in  the  presence  of  water. 

lla.  The  Manufacture  of  Aluminium 

462  The    properties  of    this  metal   which   promised   to  give   it  wide 

applicability  in  the  useful  arts,  if  it  could  be  produced  cheaply  enough, 
and  the  abundance  of  its  ores  have  led  to  innumerable  attempts,  more 
or  less  successful,  to  reduce  the  cost  of  its  production.  For  about 
thirty  years  after  its  introduction — that  is,  until  about  1885 — the  pro- 
cess of  Deville,  at  Salindres,  France,  furnished  practically  all  the 
aluminium  of  commerce.  In  this  process  the  ore  used  is  bauxite,  con- 
taining about  50  per  cent  of  aluminium  oxide,  A1208,  and  25  per  cent 
of  iron  oxide,  Fea03.  Four  steps  are  involved  in  the  process : 

(1)  The  formation  of  sodium  aluminate.     This  is  effected  by  heat- 
ing the  ore  with  sodium  carbonate  in  a  furnace.     The  reaction  is 

A1208  +  3Na2C08  =  (Na20)8Al208  +  3C02. 

The  aluminate  by  its  solubility  in  water  is  separated  from  the  iron  of 
the  ore,  the  presence  of  which  is  very  objectionable. 

(2)  The  production  of  the  oxide  free  from  iron.     This  is  accom- 
plished by  saturating  the  water  solution  with  carbon  dioxide,  when 
the  following  reaction  takes  place : 

(Na20)8Al208  +  3C02  =  A1308  +  3Na2C03. 

The  alumina  precipitates,  and  nearly  the  whole  of  the  original  carbon- 
.  ate  is  recovered  from  the  nitrate. 

(3)  The  conversion  into  chloride.      The  washed  and  partly  dried 
alumina  is  mixed  with  sodium  chloride  and  charcoal,  and  the  mixture 
is  moistened  with  water  and  worked  into  balls.     These  are  completely 
dried,  heated  to  redness,  and  treated  with  chlorine  gas.     The  following 
reaction  takes  place : 

A1208  +  30  +  601  =  AlaClc  +  3CO. 

The  chloride  and  the  salt  form  the  double  chloride  Al2016-2NaCl, 
which,  being  volatile,  distills. 

(4)  The  reduction  of  the  chloride  by  sodium.     The  double  chloride 
is  mixed  with  cryolite  (to  serve  as  flux)  and  sodium.    The  mixture 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    173 

is  quickly  introduced  into  a  red-hot  furnace,  and  the  reaction  takes 
place  with  great  energy : 

AlaCl6  +  6Na  =  2A1  +  6NaCL 

When  the  reaction  is  finished  and  the  mass  is  in  quiet  fusion,  the  melted 
metal  separates  at  the  bottom  of  the  furnace  and  is  drawn  off  and  cast 
as  desired. 

There  were  thus  produced  1,800  kilograms  in  1872,  and  the  selling  463 
price  was  $20  per  kilogram.  By  1886  the  cost  had  been  reduced  one 
half,  and  the  English  industry  was  competing  with  the  French,  but  by 
the  improved  Deville  process.  From  1883  to  1888  an  industry  was 
developing  in  Germany  which  returned  to  the  electrolytic  method  of 
Bunsen  and  Deville,  cheapened  by  the  availability  of  dynamic  elec- 
tricity. The  fused  chloride,  or  fluoride,  was  the  material  employed. 

Two  methods  of  American  origin  have  special  interest  for  their  464 
conspicuous  success.  That  of  Hall  (Pittsburg)  was  patented  in  1889. 
This  improves  the  earlier  electrolytic  methods  by  dissolving  alumina  in 
a  fused  mixture  of  aluminium  salts  and  others,  and  electrolysing  only 
the  former  without  affecting  the  solvent.  He  was  able  to  reduce  the 
price  in  1889  for  aluminium,  98  per  cent  pure,  to  $4.50,  and  later  to  $2  per 
pound,  which  in  1887  had  been  $8.  The  Cowles  (Cleveland)  process  was 
patented  in  1885.  In  this,  as  in  the  Heroult  Swiss  process,  which  dates 
from  1888,  the  aluminium  is  not  produced  pure,  but  in  alloy  with  some 
other  metal  such  as  copper.  Alumina  and  carbon,  and  the  other  metal, 
copper,  in  coarse  mixture,  are  placed  in  a  rectangular  furnace  (Cowles 
process)  so  arranged  that  the  powerful  electric  arc  from  carbon  poles 
strikes  through  the  mass.  The  great  temperature  of  the  arc  liquefies  the 
mass,  and  alumina  is  reduced,  either  by  the  action  of  the  carbon,  or  by 
electrolysis,  or  by  both  combined,  and  in  fused  condition  it  alloys  with 
the  copper  and  is  drawn  off  at  the  base  of  the  furnace,  carbon  mon- 
oxide burning  at  the  top.  (Thorpe  and  J.  W.  Richards.) 

In  1896    the  world's  production  of  aluminium  had  increased  to   465 
1,789,000  kilograms,  and  in  1897  to  3,400,000  kilograms,  and  the  price 
had  been  reduced  to  60  cents  per  kilogram.     (R.  Meyer's  Jahrbuch.) 

12.   SILICON 

Si.— 28.2 

History. — Silica,  the  oxide  of  silicon,  and  minerals  containing  it,   466 
were  used  in  remote  antiquity  for  glass-making.     It  was  long  considered 
as  an  earth  like  lime,  but  in  1660  the  fact  was  observed  that,  unlike 
such  substances,  it  could  not  neutralize  acids,  but  acted  rather  like  an 


174       ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

acid,  combining  with  alkalies.  Its  compound  nature  was  surmised  by 
Lavoisier,  but  Berzelius  in  1810  first  obtained  the  element,  although  in 
impure  condition.  In  1823  he  obtained  the  pure  substance. 

467  Natural  occurrence.  —  The  free  element  has  never  been 
found  native,  but  as  oxide,  Si02,  it  is  next  to  oxygen  the 
most  abundant  element,  constituting,  according  to  estimate, 
one  quarter  of  the  earth's  mass.     Sand,  quartz,  agate,  flint, 
and  opal  are  forms  of  silica,  while  most  rocks,  except  the 
carbonates,  are  mixed  silicates.     Silica  is  found  also  in 
plants,  especially  the  grasses,  and  in  animals  to  some  extent. 

468  Preparation.  —  It  is  obtainable  by  reaction  between  alu- 
minium, or  magnesium,  and  silica  in  the  electric  furnace  ; 
also  by  the  reducing  action  of  carbon  on  silica  at  this  high 
temperature  ;  also  by  the  action  of  aluminium  or  of  sodium 
on  silicon  chloride  : 

3SiCl4  +  4A1  =  3Si  +  2A12C16. 


But  the  processes  are  difficult,  and  the  element  is  therefore 
rare. 

469  Properties.  —  It  exists  in  three  conditions,  the  amorphous, 
the  graphitoidal  (like  graphite),  and  the  crystalline,  thus 
resembling  carbon.  The  amorphous  silicon  is  a  dark-brown 
powder,  with  the  specific  gravity  of  2.15.  It  fuses  and 
volatilizes  only  at  extremely  high  temperature.  It  is  insol- 
uble in  water  and  in  acids  other  than  hydrofluoric,  and 
soluble  in  sodium  and  potassium  hydroxides.  With  hydro- 
fluoric acid,  it  forms  hydrofluosilicic  acid,  thus  : 

Si  +  6HF  =  H2SiF6  +  4H. 
And  with  alkalies  it  forms  silicates  : 

Si  -f  2NaOH  +  H20  =  Na2Si03  +  4H. 

When  heated  in  air,  or  in  oxygen,  silicon  burns  brilliantly, 
forming  the  dioxide  Si02.  It  combines  directly  at  ordinary 
temperature  with  fluorine,  forming  SiF4,  and  with  chlorine, 


OF  THF.  \\ 

UNIVERSITY 

DESCRIPTION  OP  ELEMENTS  AND" 

when  heated,  forming  SiCl4.  Besides  the  latter  chloride, 
the  following  have  been  obtained :  Si2016,  Si3Cl8,  Si2Cl4. 
(Compare  with  the  hydrocarbons  Nos.  278  and  279.)  The 
hydride,  SiH4,  is  a  gas  which  under  some  conditions  takes 
fire  on  contact  with  air,  burning  to  water  and  silicon  diox- 
ide, Si02.  A  compound  with  carbon,  SiC,  has  already  been 
mentioned  (No.  258).  At  least  one  with  nitrogen  is  known, 
probably,  of  the  composition  Si2N3  (?),  and  one  with  sul- 
phur, SiS2.  With  many  of  the  metals  silicon  combines 
directly. 

The   crystallized   silicon    is   steel-gray    in    color,   hard  470 
enough  to  cut  glass,  has  a  specific  gravity  of  2.5,  and  is  less 
readily  acted  upon  than  is  the  amorphous. 

Silica  or  silicon  dioxide, — This  substance  is  formed  by  471 
the  oxidation  of  silicon,  and  by  the  dehydration  of  silicic 
acid.  The  native  silica,  quartz,  is  found  often  in  trans- 
parent crystals,  very  hard,  sometimes  white  and  sometimes 
tinted.  It  is  frequently  named  rock  crystal.  Amethyst, 
agate,  onyx,  flint,  hornstone,  jasper,  and  opal  are  varieties. 
It  also  exists  in  amorphous  condition,  both  native  and  arti- 
ficial, the  latter  a  fine  white  powder.  It  may  be  melted  in 
the  oxyhydrogen  flame,  and  in  the  electric  arc  it  boils  and 
volatilizes.  It  is  insoluble  in  water,  but  dissolves  in  hydro- 
fluoric acid.  If  the  latter  is  anhydrous,  the  gas,  silicon 
fluoride,  is  formed : 

Si02  +  4HF  =  SiF4  +  2H20. 

If  water  is  present,  the  fluoride  is  decomposed,  forming 
silicic  acid  and  fluosilicic  acid,  thus  : 

2SiF4  +  3H20  =  H2Si03  +  H2SiF6  +  2HF. 

It  is  by  virtue  of  these  reactions  that  hydrofluoric  acid  at-  472 
tacks  glass,  which  is  a  mixture  of  silicates.     The  amor- 
phous  silica   dissolves    in    the    alkaline   hydroxides,   only 
slightly  in  that  of  ammonium,  also  to  some  extent  in  the 
alkaline  carbonates,  in  both  cases  forming  soluble  alkaline 


176        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

silicates,  in  which  it  acts  as  acid.  In  one  compound — 
namely,  Si02-P205'4H20 — it  would  seem  to  act  as  base  to 
phosphorus  pentoxide,  which  is  certainly  acid  (Haute- 
feuille). 

473  Silicic  acid  and  the  silicates. — Silica  is  an  acid-forming 
oxide,  combining   with  water  in  varying  proportion,  and 
forming  a  series  of  silicic  acids.     The  simplest  one — and  it 
may  be  taken  as  typical  of  the  rest — is  H2O.Si02,  or  H2Si03, 
sometimes  designated  as  metasilicic  acid.     This  is  obtained 
as  a  white  gelatinous  precipitate  by  adding  hydrochloric  or 
other  acid  to  a  solution  of  alkaline  silicate  : 

Na2Si03  +  2HC1  =  H2Si03  +  2NaCl. 

This  precipitate  is  soluble  in  sodium  and  potassium  hydrox- 
ides, and  in  excess  of  hydrochloric  acid,  less  so  in  ammo- 
nium hydroxide.  By  drying  and  heating,  it  loses  its  water, 
and  the  anhydrous  silica  does  not  dissolve  by  hydrochloric 
acid.  The  silicic  acid  may  also  be  obtained  in  a  form  which 
is  soluble  in  water,  but  which  is  unstable  and  is  thrown 
into  the  insoluble  form  by  the  presence,  even  in  small  quan- 
tity, of  various  substances,  the  change  liberating  heat. 
Whether  this  is  an  allotropic  form  or  a  different  hydrate  is 

474  not  known.     Silicon  dioxide  combines  with  metallic  oxides 
in  great  variety  of  ratio  and  complexity,  forming  the  almost 
innumerable  silicates  which  make  up  the  greater  part  of 
the  earth's  crust.     The  silicates  of  the  alkalies,  sodium  and 
potassium,  are  soluble  in  water,  although  in  solution  they 
are  decomposed  by  carbonic  acid,  and  even  by  water  itself 

.  in  dilute  solution,  for  the  silicic  is  a  very  feeble  acid.  To 
keep  them  in  solution,  therefore,  requires  some  excess  of 
the  alkali  base.  Silica  occurs  in  some  natural  waters,  either 
as  soluble  silicic  acid  or  as  alkaline  silicate.  To  the  slow 
deposition  of  silica  from  such  solution  is  due  probably  the 
formation  of  silicified  or  petrified  wood  and  shells,  very 
beautiful  samples  of  which  are  often  found.  The  non-alka- 
line silicates  are  insoluble  in  water. 


DESCRIPTION  OF  ELEMENTS  AND   COMPOUNDS    177 

The  comparison  of  silicon  with  carbon  is  extremely  in-  475 
teresting ;  in  its  predominating  quantity  and  in  the  char- 
acteristics which  it  imparts  to  its  compounds,  the-  former 
seems  to  bear  much  the  same  relation  to  the  mineral  world 
that  carbon  bears  to  the  world  of  living  things. 

12a.  Some  Uses  of  the  Silicates 

Soluble  glass. — This  is  sodium  or  potassium  silicate,  or  a  mixture  of  476 
the  two.  It  is  made  by  fusing  3  parts  of  silica  mixed  with  2  parts  of 
potassium  carbonate,  or  with  3  parts  of  sodium  carbonate  ;  or  by  heat- 
ing silica  with  a  solution  of  caustic  alkali  under  pressure.  It  forms  a 
transparent  non-crystalline  mixture,  which  is  soluble  in  water.  If  the 
proportion  of  silica  is  increased  the  fusing  point  is  raised,  and  the 
product  is  not  completely  soluble  in  water.  It  is  used  as  a  cement, 
especially  in  the  making  of  artificial  stone;  also  as  a  constituent  of 
paints,  particularly  the  fireproof  paints ;  and  it  is  sometimes  put  into 
soaps. 

Glass. — The  origin  of  glass-making  is  lost  in  antiquity.  In  Egyp-  477 
tian  tombs  have  been  found  articles  of  glass  and  pictures  of  men  who 
are  engaged  in  glass-making  and  glass-blowing,  showing  that  the  art 
must  have  been  invented  before  2000  B.  c.  An  urn  of  white  glass, 
ornamented  with  colored  glass,  dating  from  the  seventeenth  century 
B.  c.,  has  been  found,  and  glass  lenses  have  been  discovered  at  Nineveh. 
Aristophanes,  a  Greek  writer,  refers  to  the  use  of  a  glass  lens  as  burn- 
ing glass.  Cicero  mentions  Egyptian  glass,  and  in  the  time  of  Au- 
gustus tribute  was  paid  in  glass,  so  highly  was  it  valued.  At  Hercula- 
neum  and  Pompeii  window  glass  has  been  discovered  which  was  made 
by  "  blowing."  Glass  was  used  in  church  windows  as  early  as  A.  D.  674. 
In  the  sixteenth  and  seventeenth  centuries  Venetian  glass,  especially 
that  of  Murano,  became  famous  throughout  the  civilized  world.  In 
the  sixteenth  century  the  Bohemian  industry  began  to  flourish,  favored 
by  the  accessibility  of  unusually  pure  material.  Bohemian  glass  is  still 
preferred  for  chemical  ware,  owing  to  its  resistance  to  corrosion  by 
reagents.  The  famous  plate-glass  industry  of  France  was  started  in 
1688. 

Glass  is  a  mixture  of  silicates,  varying  only  as  to  the  bases.    Soda-   478 
lime  silicate  is  used  in  window  and  in  bottle  glass,  which,  in  the  cheaper 
grades,  is  tinted  green  by  the  presence  of  iron.     Potash-lime  silicate  is 
used  in  the  Bohemian,  in  the  German  plate,  and  in  the  French  crown 
glass.    It  is  less  fusible  and  less  acted  upon  than  the  soda-lime  glass. 


178        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

In  flint  glass  or  crystal  the  base  is  lead  and  potash  or  soda.  This 
variety  has  a  higher  specific  gravity,  luster,  and  refractive  power,  and 
is  more  fusible  and  more  easily  acted  upon  than  the  others. 

479  For  silica,  sand  is  used,  which  for  any  but  the  cheaper  grade  of  glass 
must  be  free  of  iron.     Sometimes  arsenious  oxide,  or  manganese  dioxide, 
or  potassium  nitrate  is  used  to  counteract  the  effect  of  the  iron.     The 
alkali,  if  potassium,  is  used  as  carbonate ;  if  sodium,  it  is  used  as  car- 
bonate, or  as  the  sulphate  which  is  produced  in  one  stage  of  the  Le- 
blanc  process.     The  attempts  to  use  the  cheaper  chloride  have  not  been 
successful.     The  lead  is  supplied  usually  as  red  lead  or  minium,  Pb804. 
For  the  lime  either  chalk  or  limestone  is  used. 

480  Glass  is  made  white  and  translucent  by  adding  a  mixture  of  tin 
and  lead,  or  by  adding  arsenic  or  bone  ash  (calcium  phosphate)  or 
fluorides,  such  as  calcium  fluoride.     Colored  glasses  are  made  by  the 
addition  of  various  metallic  oxides  in  small  quantity — blue  by  cop- 
per or  cobalt ;  amethyst  by  manganese ;  green  by  a  mixture  of  iron 
and  copper;  yellow  sometimes  by  adding  wood  (i.  e.,  carbon),  some- 
times by  sulphur. 

481  The  process  consists  in  heating  the  suitable  mixture  in  pots  of  fire- 
clay to  a  high  temperature.     Broken  glass  is  usually  mixed  with  the 
new  material  in  order  that  fusion  may  be  brought  about  without  too 
high  a  temperature  which  causes  waste  of  alkali  before  the  reaction 
sets  in.     The  escape  of  carbon  dioxide,  and  of  sulphur  dioxide  if  sul- 
phate is  used,  causes  effervescence.     After  the  reaction  is  complete  the 
mixture  is  kept  in  fusion  until  the  impurities  come  to  the  top  and  form 
the  scum  which  is  removed.     The  glass  in  a  semi-solid  or  plastic  condi- 
tion is  worked  into  the  desired  shape  by  many  ingenious  methods, 
which,  however,  do  not  involve  chemical  processes. 

482  Porcelain  and  earthenware. — In  the  making  of  these  materials,  which 
also  is  a  very  ancient  art,  advantage  is  taken  of  two  properties  shown 
by  the  natural  substance,  clay  ;  one  is  that  of  plasticity  when  wet,  and 
the  other  is  that  of  hardening  by  heat.     Clay  in  its  several  varieties  is 
the  product  by  slow  natural  decomposition  of  the  mineral  feldspar,  a 
common  rock.     Pure  feldspar  is  a  silicate  of  aluminium  and  sodium  or 
potassium.     By  its  decomposition  the  alkaline  silicate  is  washed  out 
and  aluminium  silicate  is  left.     This  substance  is  known  as  kaolin,  and 
in  some  places  is  found  very  pure.     It  is  greatly  prized  as  material  for 
the  finer  porcelains.     Common  clay  consists  of  kaolin  mixed  with  more 
or  less  of  other  substances — carbonates  of  calcium  and  magnesium,  iron 
oxide,  silica,  etc.     For  fine  porcelain  the   white  powdered  kaolin  is 
mixed  with  some  more  fusible  substances,  such  as  feldspar,  chalk,  or 
gypsum  (calcium  sulphate),  worked  into  plastic  mixture  with  water, 


DESCRIPTION  OF  ELEMENTS  AND   COMPOUNDS    179 

formed  into  desired  shapes,  and  heated  in  a  furnace  to  high  tempera- 
ture, when  the  more  fusible  portion,  the  flux,  melts  and  cements  the 
whole  into  a  hard,  translucent  material.  This  is  less  corroded  by 
chemicals  and  less  liable  to  crack  by  heating  than  is  glass,  and  so  is  a 
material  very  useful  for  chemical  operations.  The  factories  of  Meissen 
and  of  Berlin  are  famous  for  their  chemical  ware,  while  Sevres  and 
others  are  noted  for  artistic  porcelains. 

Stoneware  is  distinguished  from  porcelain  in  being  opaque,  for  it  is  483 
not  heated  to  so  high  a  temperature,  and  the  flux  does  not  penetrate 
the  material  as  in  porcelain.  Earthenware  is  of  common  clay  and  is 
hardened  by  heat  without  fusion,  and  therefore  remains  porous.  The 
surface  may  be  glazed  by  a  subsequent  operation.  This  is  sometimes 
accomplished  by  throwing  salt  into  the  oven  at  the  end  of  the  firing. 
The  salt  volatilizes,  is  decomposed,  and  sodium  aluminium  silicate  is 
formed  and  fused  on  the  surface.  Bricks,  terra-cotta,  and  tiling  are  of 
the  same  general  character  (Roscoe  and  Thorpe).  The  use  of  sand  in 
mortar  and  cement  will  be  referred  to  in  connection  with  calcium. 


13.  PHOSPHORUS 

P.— 30.8 

History. — Phosphorus  was  discovered  by  the  alchemist  Brand,  of   484 
Hamburg,  in  1669.     For  many  years  it  remained  a  rare  and  costly 
curiosity.     In  1771,  Scheele,  a  Swede,  made  it  from   bone  ash  and 
greatly  reduced  the  cost.    This  still  remains  the  commercial  source  of 
the  element. 

Natural  occurrence. — Free  phosphorus  is  not  found  na-  485 
tive,  owing  to  its  readiness  of  oxidation.  As  pentoxide, 
P206,  it  exists  in  all  phosphates,  particularly  in  the  min- 
erals phosphorite  and  apatite,  which  are  phosphates  of  cal- 
cium. As  such  it  is  also  a  constituent  of  fertile  soils  and 
of  natural  waters.  It  is  an  essential  element  in  plants, 
being  contained  especially  in  fruits  and  seeds.  In  animals 
it  is  a  part  of  the  brain  and  nerve  substance,  and,  as  cal- 
cium phosphate,  constitutes  nearly  the  whole  of  bone  ash. 
It  is  a  waste  product  of  the  tissue  which  is  consumed 
in  the  animal  organism,  and  it  is  excreted  as  sodium 
ammonium  phosphate.  It  has  been  found  in  meteoric 
stones. 

18 


180        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

485/1  Preparation. — Phosphorus  is  prepared  by  removing  the 
oxygen  from  the  pentoxide  contained  in  a  phosphate. 
The  reducing  substance  is  commonly  carbon.  For  more 
detailed  description  see  Xo.  499. 

486  Properties. — It  exists  in  at  least  two  allotropic  forms, 
commonly  designated  as  the  yellow  and  the  red.     The  so- 
called  yellow  phosphorus,  before  it  has  been  exposed  much 
to  the  light,  is  white  and  translucent,  somewhat  like  par- 
affin in  appearance.     By  exposure,  the  surface  film  becomes 
opaque,  while  the  interior  may  still  be  translucent,  but 
reddish  yellow.     By  long  exposure  the  color  deepens.     At 
about  15°,  phosphorus  in  hardness  and  consistency  resem- 
bles wax,  but  at  lower  temperature  it  is  brittle.     Its  specific 
gravity  is  1.8  (H20  =  1).    For  its  peculiarity  of  vapor-density 
compare  No.  93.     Under  water  it  melts  at  44°,  but  other- 
wise at  30°,  and  at  34°  in  air  it  takes  fire.     It  sublimes  at 
ordinary  temperature,  if   in   a   vacuous   tube,   and   forms 
white  rhombic  crystals.     In  a  non-oxidizing  atmosphere  it 
boils  at  269°,  and  its  vapor  is  colorless  (Eeadman-Thorpe). 
It  is  reckoned  as  insoluble  in  water,  yet  it  imparts  its  pecul- 
iar odor  to  water  in  which  it  has  been  immersed ;  and  if 
the  water  which  covers  the  phosphorus  is  boiled,  the  latter 
slowly  distills  with  the  steam.     It  is  very  soluble  in  carbon 
disulphide,  from  which  it  may  be  crystallized. 

487  It  ignites,  as  already  stated,  at  a  very  low  temperature, 
and  burns  with  a  bright,  white  light,  the  chief  product  being 
P205.     It  is  necessary  to  keep  it  and  manipulate  it  under 
water,  and  the  utmost  caution  against  fire  must  be  exer- 
cised in  its  use.     When  exposed  to  moist  air  it  gives  out  a 
feeble  light  which  may  be  seen  in  a  darkened  room.     In- 
deed, it  took  its  name,  signifying  light-bearer,  from  this 

488  property  which  is  called  phosphorescence.     It  is  supposed  to 
be  due  to  slow  oxidation,  but,  singularly,  it  does  not  show  in 
absolutely  dry  air,  nor  in  moist  air,  below  0°,  or  at  increased 
pressure,  nor  in  pure   oxygen  below  15°,  if  at  ordinary 
pressure ;  but  if  the  pressure  is  reduced,  luminosity  returns. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    181 

The  phosphorescence  is  thought  to  be  somehow  associated 
with  the  formation  of  ozone  (or  of  peroxide  of  hydrogen), 
since  it  is  prevented  by  the  presence  in  traces  of  such  sub- 
stances as  destroy  ozone.  It  decomposes  water  when  heated 
with  steam  to  250°.  It  combines  directly  with  fluorine, 
chlorine,  bromine,  iodine,  forming  PF3,  FF5,  PC13,  PC15, 
PBr3,  PBr5,  and  PI3 ;  also  with  sulphur  in  a  great  variety 
of  proportions,  including  P2S3  and  P2S5 ;  with  most  of  the 
metals,  forming  phosphides,  e.  g.,  Na3P  and  K3P.  No  com- 
pound with  carbon  nor  with  silicon  is  known,  and  the  exist- 
ence of  one  with  nitrogen  is  not  fully  established.  With 
hydrogen,  PH3  and  others  are  known. 

Phosphorus  (the  yellow)  is  extremely  poisonous,  one  489 
tenth  of  a  gram  proving  fatal.  In  much  smaller  doses  it 
is  used  as  a  medicine.  Those  who  are  habitually  exposed 
to  its  fumes  are  subject  to  a  dreadful  disease  which  results 
in  the  rotting  of  the  bones  of  the  jaw  and  nose.  Burns 
made  by  it  are  very  painful  and  difficult  to  heal. 

Red  phosphorus. — When  the  yellow  phosphorus  is  490 
heated,  not  in  contact  with  oxygen,  to  240°  or  250,°  it  is 
changed  to  an  allotropic  form  known  as  red  or  amorphous 
phosphorus.  A  lower  temperature  brings  the  same  result 
if  a  trace  of  iodine  is  present,  and  a  higher  temperature  and 
pressure  hasten  the  change.  Other  conditions  also  bring 
it  about  to  some  extent.  It  appears  as  a  reddish-brown 
powder,  or  in  hard,  brittle,  opaque  lumps  of  the  same  color. 
It  may  be  crystallized  by  heating  under  pressure  to  580°, 
when  it  melts  and,  on  solidifying,  crystallizes.  It  has  no 
odor,  and  does  not  fume  nor  phosphoresce.  It  does  not  dis- 
solve in  carbon  disulphide  nor  in  other  solvents.  Its  spe- 
cific gravity  is  2.25. 

At  about  the  temperature  of  its  production,  260°,  it  491 
changes  back  to  the  yellow  form  with  the  liberation  of  heat. 
It  does  not  ignite  below  240°,  and  is  much  less  reactive 
than  the  yellow.     It  is  not  poisonous,  being  excreted  appar- 
ently without  absorption  or  change. 


182        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

13a.  The  Oxides  of  Phosphorus  and  their  Acids 

492  The  following  oxides  and  acids  have  been  described : 

Oxides.  Acids. 

P40  No  acid. 

P20  *  P20  •  3H20,  hypophosphorous  acid. 

P^e  P2(V3H20,  phosphorous  acid. 

Ps04  P204  •  2H20,  hypophosphoric  acid. 

P4010  P205-3H20,  phosphoric  acid. 

The  only  ones  which  call  for  consideration  here  are 
the  phosphorous  or  trioxide,  and  the  phosphoric  or  pent- 
oxide. 

493  Phosphorous  oxide,  P406. — This  is  formed  by  the   slow 
oxidation  of  phosphorus  at  low  temperature,  and  by  the 
burning  of  phosphorus  with  insufficient  oxygen ;  and  it  is 
separated  by  its  greater  volatility  from  the  pentoxide  which 
is  formed  at  the  same  time.     It  is  a  white  crystalline  solid, 
which  melts  at  22.5°  and  boils  at  1738.     Its  vapor-density 
indicates  the  formula  P406.      It  has  the  garliclike  odor 
which  is  associated  with  phosphorus,  and  it  is  very  poison- 
ous.    With  cold  water  it  slowly  combines,  forming  phos- 
phorous acid,  H3P03 ;  with  hot  water  it  combines  violently, 
with  some  decomposition.     By  heating  to  440°,  it  is  entirely 
decomposed  into  the  tetroxide,  P204,  and  red  phosphorus. 
By  slight  warming  in  contact  with  air  it  inflames,  burning 
to  the  pentoxide. 

494  Phosphoric  oxide,  P4010. — This  is  a  white,  odorless,  amor- 
phous solid,  volatile  below  red  heat.     Its  vapor-density  indi- 
cates the  formula  P4010  (Tilden,  1896).     It  is   extremely 
deliquescent,  being  the  most  effective  drying  agent  known. 
With  water  it   forms   at  least   three  different  acids.     By 
deliquescence  in  moist  air  metaphosphoric  acid  is  formed. 
This,  by  boiling  with  excess  of  water,  yields  orthophosphoric 

*  Besson,  Coraptes  Rendus,  124,  1897, 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    183 

acid,  and  this  in  turn,  by  evaporating  the  excess  of  water 
and  heating  the  acid  to  about  215°,  is  converted,  although 
not  completely,  into  the  pyrophosphoric '  acid.  The  relation 
of  the'three  acids  may  be  seen  in  the  following  equations  : 

P205  +  H20    =  H2P206 ,  metaphosphoric  acid. 

P205  -(-  2H20  =  H4P207 ,  pyrophosphoric  acid. 

PA.+  3H20  =  H6P208  =  2H3P04,  orthophosphoric  acid. 

Orthophosphoric  acid  may  be  obtained  in  crystallized  495 
condition  by  the  evaporation  of  its  water  solution,  and  the 
pyrophosphoric  maybe  obtained  in  the  form  of  an  amorphous, 
glasslike  substance,  or  it  may  be  crystallized.  Both  are 
non-volatile  (?).  The  metaphosphoric  acid  appears  in  com- 
merce as  a  white,  glasslike  'solid,  called  "  glacial  phosphoric 
acid."  It  is  volatile  at  a  bright-red  heat,  and  its  vapor- 
density  indicates  the  formula  H2P206  (Tilden,  1896).  All 
these  acids  form  salts,  the  most  important  being  the  ortho- 
phosphates,  and  of  these  the  calcium  salt  is  perhaps  the 
most  important.  The  hydrogen  of  the  orthophosphoric 
acid,  H3P04 ,  may  be  substituted  by  metal  in  thirds  at  a 
time,  so  that  with  sodium,  for  example,  the  three  salts  are 
obtained,  ]STaH2P04,  Na2HP04,  and  Na3P04. 

13b.   Other  Compounds  of  Phosphorus 

Hydrides. — That  hydrogen  and  phosphorus  combine  496 
directly  has  been  stated  and  denied.  However,  the  com- 
pound, PIT3,  phosphorus  trihydride,  or  phosphine,  or  phos- 
phureted  hydrogen,  has  been  obtained  by  other  means.  It 
is  formed  by  the  action  of  water  on  some  metallic  phos- 
phides, as  ammonia  is  formed  by  the  action  of  water  on 
some  metallic  nitrides ;  also  by  boiling  phosphorus  with 
sodium  or  potassium  hydroxide  solution..  It  is  a  gas  with 
a  garliclike  odor,  only  slightly  soluble  in  water,  easily  com- 
bustible, with  no  action  on  litmus,  but  acting  as  a  feeble 
base  in  combining  with  some  acids — e.  g.,  hydrochloric, 


184        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

forming  a  salt,  PH3HC1,  analogous  to  ammonium  chloride, 
NH3HC1,  and  named  phosphonium  chloride. 

Another  hydride,  P2H4  (compare  N2H4),  is  a  liquid  at 
ordinary  temperature,  and  its  vapor  inflames  on  Contact 
with  air.  A  third  (P4H2  ?)  of  undetermined  composition  is 
solid  at  ordinary  temperature.  The  existence  of  another 
solid  hydride,  P3H,  has  been  claimed  by  some. 

497  Chlorides. — The  trichloride,  PC13,  is  a  colorless  liquid, 
and  the  pentachloride  a  yellowish  solid.     Both  are  formed 
by  direct  union  with  chlorine,  and  both  react  energetically 
with  water,  forming  phosphorous  and  phosphoric  acids  : 

PC13  +  3H20  =  H3P03  +  3HC1. 
PC15  +  4H20  =  H3P04  +  5HC1. 

13c.  The  Manufacture  of  Phosphorus  and  of  Matches 

498  The  crude  phosphates. — Commercial  bone  ash  contains  from  27  to 
37  per  cent  of  phosphorus  pentoxide  as  tricalcium  phosphate,  Ca3  (P04)2, 
a  salt  insoluble  in  water.     This  material  is  especially  preferred  in  mak- 
ing phosphorus.     A  similar  crude  phosphate  is  obtained  as  a  by-product 
in  making  glue ;  for  the  bones  are  treated  with  dilute  hydrochloric 
acid,  which  dissolves  out  the  inorganic  portion,  Ca3(P04)2,  leaving  the 
organic  part,  from  which  the  glue  is  made.     From  this  acid  solution, 
calcium  phosphate  is  precipitated  by  adding  limewater.     The  native 
calcium  phosphates,  more  or  less  impure,  known  as  apatite  and  phos- 
phorite, are  available.     The  former  is  found  in  Spain,  France,  West 
Indies,  Canada,  South  Carolina,  Florida,  and  elsewhere.     A  phosphate 
of  aluminium  and  iron  from  the  West  Indies  is  another  source. 

499  Phosphorus-making.— Whatever  the  crude  material,  it  is  finely  ground 
and  mixed  with  crude  sulphuric  acid  in  vats  made  of  wood,  heavily  oiled 
for  protection.    Sufficient  acid  is  added  for  the  following  reaction : 

Ca3(P04)2  +  3HaS04  =  2H3P04  +  3CaS04. 

After  the  mixture  has  been  thoroughly  stirred  for  some  time,  the  in- 
soluble calcium  sulphate  is  separated  by  filtration  through  beds  of 
ashes,  is  washed  with  water,  and  then  drained  and  dried.  It  is  tech- 
nically known  as  "sludge,"  and  is  used  in  making  fertilizers.  The 
acid  liquor  is  concentrated,  mixed  with  coarsely  ground  charcoal  or 
coke,  or  with  sawdust,  and  still  further  dried.  It  is  then  transferred  to 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    185 

retorts  of  fire-clay,  holding  from  20  to  30  pounds,  and  brought  to  a 
high  temperature,  nearly  white  heat.  The  orthophosphoric  acid  is  thus 
first  converted  into  the  meta  acid,  and  this  is  reduced  by  the  carbon  as 

thus  expressed : 

H2Pa06  +  6C  =  2P  +  6CO  +  2H. 

The  phosphorus  distills  from  the  retort,  and  is  condensed  under  water.  500 
It  is  purified  by  redistillation  in  an  iron  retort,  or  by  treatment  under 
water  with  dilute  sulphuric  acid  and  potassium  bichromate,  and  filtra- 
tion through  canvas.  It  is  then  remelted  and  cast  in  desired  form, 
always  under  water,  and  packed  in  tin  cans,  which  are  filled  with  water 
and  hermetically  sealed. 

A  more  recent  method,  made  practicable  by  cheapened  electricity,  501 
uses  the  latter  as  source  of  heat  in  a  modified  electric  furnace.  The 
mixture  of  crude  phosphate,  carbon,  and  a  flux  (kaolin  or  sand),  is  fed 
into  the  furnace  and  heated  directly  by  the  electric  arc  ;  the  phosphorus 
and  other  gases  are  distilled  off,  and  the  melted  residue  or  slag  is 
drawn  off  at  the  bottom.  The  process  may  thus  be  carried  on  contin- 
uously for  days.  Phosphorus  is  largely  consumed  in  the  manufacture  of 
matches.  In  smaller  quantity  it  is  used  in  medicine,  in  the  laboratory, 
and  in  various  other  ways.  (Headman-Thorpe.) 

Fertilizers. — It  has  been  stated  that  phosphate  is  a  constituent  of  502 
fertile  soil,  being  taken  up  by  plants  as  a  necessary  part  of  their  food. 
It  is  important,  therefore,  to  restore  to  the  soil  that  which  is  thus  taken 
from  it.  This  is  done  by  phosphate  fertilizers  which  supply  calcium 
phosphate  in  one  form  or  another.  Besides  the  phosphates  already  men- 
tioned as  crude  material  in  preparing  the  element,  the  phosphates  from 
some  other  sources  are  utilized.  Guano  is  the  excrement  and  carcasses 
of  sea  fowl,  more  or  less  modified  by  time  and  exposure.  It  is  found 
in  large  deposits  in  Peru,  Chili,  and  in  other  portions  of  South  Amer- 
ica, in  South  Africa,  and  elsewhere.  From  some  of  this  material,  the 
nitrogenous  content  has  been  washed  out  and  the  residue  is  rich  in 
calcium  phosphate,  sometimes  containing  as  much  as  35  per  cent  of 
the  pentoxide.  PJiosphatic  slag  is  a  waste  material  produced  in  the 
removal  of  phosphorus  from  pig-iron  by  means  of  lime.  This  contains 
from  10  to  25  per  cent  of  pentoxide,  mainly  as  the  calcium  salt,  and  has 
been  successfully  utilized  as  fertilizer.  Practically  all  of  these  crude  503 
materials  furnish  only  the  tricalcium  phosphate,  Ca3(P04)2,  which  is  in- 
soluble in  water.  Some  of  them,  especially  the  guanos,  slag,  and  bone 
ash,  may  be  applied  to  the  soil  without  other  treatment  than  pulveriz- 
ing. But  others,  like  the  rock  phosphates,  are  treated  with  sulphuric 
acid  after  fine  grinding,  and  the  phosphate  is  changed  to  the  monocal- 
cium  salt  which  is  soluble  in  water,  and  therefore  more  quickly  and 


186        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

uniformly  distributed  through  the  soil  and  taken  up  by  plants.  The 
reactions  involved  are  seen  in  the  following  equations : 

(1)  Cas(P04)3  -I-  2H9S()4  =  CaH4(P04)a  +  2CaS04. 

(2)  Ca,(P04)9  +  3H2S04  =  2H3P04  +  3CaS04. 

(3)  Ca8(P04)2  +  HaS04  =  Ca,H,(P04)i  +  CaS04. 

The  aim  is  to  bring  about  the  first  reaction  chiefly,  but  the  second  is 
allowed  to  take  place  to  some  extent.  The  dicalcium  salt  is  insoluble, 
and  therefore  nothing  is  gained  by  the  third  reaction.  The  soluble 
salt  produced  in  the  process  is  called  technically  superphosphate.  Be- 
fore using  the  sulphuric  acid,  the  crude  material  is  dried  and  very 
finely  powdered.  It  is  then  thoroughly  mixed  with  the  acid  in  suitable 
quantity.  After  the  reaction  is  over,  the  mixture  solidifies.  It  is 
further  dried  at  about  105°  and  again  ground  to  powder,  when  it  is 

504  ready  for  the  market.     The  product  on  keeping  is  subject  to  a  change 
called  "  reversion,"  which  takes  place  if  iron  oxide  or  alumina  is  pres- 
ent, and  the  result  of  which  is  that  the  soluble  phosphate  passes  back 
into  the  tri calcium  salt,  and  insoluble  phosphate  of  iron  or  of  aluminium 
is  produced.     These,  although  not  useless,  are  less  valuable  than  the 
superphosphate  (Warington- Thorpe). 

505  Matches. — Phosphorus  was  first  used  for  making  matches,  according 
to  some,  in  1805  in  Paris.     By  others  it  is  stated  that  the  first  friction 
matches  containing  it  were  made  in  1816,  also  in  Paris.     Other  chem- 
ical methods  of  getting  fire  had  been  devised,  but  without  general  suc- 
cess, and  the  method  by  friction  of  flint  and  steel  was  the  only  one  in 
general  use  up  to  1820,  and  indeed  was  not  entirely  displaced  so  late 
as  1840.     The  "  Lucifer  match  "  in  its  original  form,  invented  by  an 
Englishman  in  1827,  contained  no  phosphorus,  the  splints  of  wood  being 
tipped  with  a  mixture  of  antimony  sulphide,  potassium  chlorate,  gum, 
and  starch,  and  ignited  by  rubbing  on  glass  or  sandpaper.    The  first 
attempts  to  use  phosphorus  were  not  very  successful,  but  in  1834  the 
German  makers  reached  better  results  and  phosphorus  friction  matches 
came  into  more  general  use.     An  improvement  made  in  1835  consisted 
in  using  red  lead,  Pb304,  and  manganese  dioxide,  Mn09,  as  oxidizing 
material  with   the  phosphorus.     The  first  patent  of  this  kind  in  the 
United  States  was  granted  in  1836  for  a  mixture  of  phosphorus,  sulphur, 
chalk,  and  glue.     The  manufacture  rapidly  increased,  and  the  danger 
of  accidental  ignition  of  phosphorus  mixtures,  and  the  terrible  disease 
which  made  its  appearance  among  the  workers  in  phosphorus,  attracted 
great  attention.     Investigation  showed  that  the  latter  was  probably  due 
to  the  direct  action  of  the  fumes  of  phosphorus  (i.  e.,  P40«)  on  the  bone 
itself,  and  that  it  attacked  only  those  whose  teeth  were  decayed.    As  a 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    187 

result,  improved  ventilation,  cleanliness,  and  strict  attention  to  sanitary 
conditions  have  almost  eliminated  the  disease.  After  the  discovery  of  506 
red  phosphorus  in  1845,  attempts  were  quickly  made  to  take  advantage 
of  its  non-poisonous  character  and  less  inflammability  by  substituting 
it  for  the  yellow  variety.  In  1855,  and  in  Sweden,  the  first  "  safety 
matches  "  were  made.  The  invention  consisted  in  putting  the  oxidizing 
mixture  on  the  match  head,  and  the  red  phosphorus  on  the  box  surface. 
The  match  could  be  ignited  only  by  friction  on  the  latter.  One  recipe 
gives  for  the  mixture  on  the  match  head,  antimony  sulphide  8  parts, 
potassium  chlorate  8  parts,  red  lead  8  parts,  and  gum  1  part ;  on  the 
rubber,  red  phosphorus  1  part,  antimony  sulphide  7  parts,  glue  1  part, 
and  powdered  glass  3  parts.  Such  matches  are  now  made  in  great 
quantity  in  Sweden.  As  typical  of  a  match  prepared  to  ignite  without 
the  specially  prepared  surface  may  be  cited  this  recipe :  Red  phosphorus 
1  part,  potassium  chlorate  6  parts,  red  lead  2  parts,  glue  1  part,  pow- 
dered glass  3  parts,  clay  3  parts  (Clayton-Thorpe). 


14.   SULPHUR 

S.-31.83 

Natural  occurrence. — Sulphur,  being  quite  common  in  the  507 
free  state,  has  been  known  from  the  earliest  times.  It  is 
found  in  the  neighborhood  of  extinct  and  of  active  volcanoes 
— e.  g.,  in  Italy,  Sicily,  California,  and  in  the  Yellowstone 
region.  The  native  sulphides  are  abundant,  many  of  the 
most  common  metallic  ores  being  of  this  form — e.  g.,  sul- 
phide of  iron  (known  as  pyrites),  of  copper,  lead,  zinc,  and 
mercury.  Native  sulphates  also  are  common,  such  as  sul- 
phate of  calcium  (known  as  gypsum],  of  barium,  and  of 
magnesium.  Volcanic  gases  often  contain  sulphur  dioxide, 
and  some  contain  hydrogen  sulphide.  Besides  this,  sul- 
phur is  a  constituent  of  many  substances  of  plant  and  of 
animal  origin — e.  g.,  mustard,  garlic,  bile,  albumin,  and  pro- 
toplasm itself. 

Preparation. — Native  sulphur  is  refined  by  fusion  or  by  508 
distillation,  and  comes  into  commerce  as  roll  sulphur  or 
brimstone,  as  sulphur  flowers  (the  sublimate),  and  as  milk 
of  sulphur  (precipitated  sulphur). 


188        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

509  Properties. — Sulphur  exists  in  at  least  three  allotropic 
forms — the  rhombic,  the  monoclinic  (referring  to  crystal- 
line form),  and  the  plastic. 

509/1  Rhombic  or  common  sulphur. — Sulphur  in  this  form  is 
deposited  by  crystallization  from  solution  in  carbon  disul- 
phide.  It  is  yellow,  has  the  specific  gravity  2.05,  is  insol- 
uble in  water,  and  melts  at  114°. 

509/2  Monoclinic  sulphur  is  obtained  by  crystallization  from 
fusion,  and  from  solution  in  some  solvents.  Its  specific 
gravity  is  1.96,  and  it  is  soluble  in  carbon  disulphide. 
This  form  is  not  stable  at  ordinary  temperature,  but 
changes  into  the  rhombic ;  as  a  result,  the  crystals,  which 
are  at  first  clear  and  transparent,  become  opaque,  owing  to 
their  breaking  up  into  minute  crystals  of  the  other  variety, 
although  the  external  form  is  preserved.  This  change  is 
accompanied  by  the  liberation  of  heat.  On  the  other  hand, 
the  rhombic  crystal  is  similarly  changed  into  monoclinic 
when  kept  at  a  temperature  between  100°  and  114°. 

509/3  Plastic  sulphur. — Sulphur  melts  to  an  amber-colored 
liquid,  which,  as  the  heating  is  continued,  becomes  of  a 
dark-red  color,  and  suddenly  changes  to  a  thick,  semi-solid 
condition.  On  further  heating,  it  again  liquefies  and  finally 
begins  to  boil.  If  at  this  stage  it  is  suddenly  cooled  by 
pouring  into  water,  it  becomes  a  transparent,  plastic,  rub- 
berlike  substance.  This  is  the  amorphous  or  plastic  sul- 
phur. It  is  not  stable,  but  changes  in  a  few  hours,  or 
quickly  if  warmed  to  100°,  back  to  the  brittle,  common 
form.  The  plastic  allotrope  has  the  specific  gravity  1.95, 
and  is  insoluble  in  carbon  disulphide.  Some  describe  an- 
other allotrope,  which  is  white,  amorphous,  present  in  the 
sublimate,  but  not  soluble  in  carbon  disulphide,  and  con- 
vertible at  100°  into  the  common  form ;  and  still  another 
which  is  soluble  in  water. 

509/4  Sulphur,  of  all  varieties,  boils  at  446°,  and  gives  an 
orange-colored  vapor.  The  peculiarities  of  its  specific 
gravity  in  gaseous  condition  have  been  elsewhere  described 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    189 

(see  No.  93).  It  ignites  easily  and  burns  with  a  pale-blue 
flame;  the  product  of  combustion  is  the  dioxide,  S02. 
Sulphur  combines  directly  also  with  hydrogen,  boron  (B2S3), 
carbon  (CS2),  chlorine,  bromine,  iodine,  and  probably  fluor- 
ine, with  phosphorus,  and  with  many  metals ;  in  addition, 
compounds  with  nitrogen  (N4S4),  and  with  silicon  (SiS) 
and  (SiSg),  are  formed,  although  not  by  direct  action. 

14a.  Compounds  with  Hydrogen  and  with  Chlorine 

Hydrogen  sulphide,  or  hydrosulphuric  acid,  or  sulphu-  510 
reted  hydrogen,  H2S. — This  substance  occurs  native  to  some 
extent  in  volcanic  gases,  in  mineral  waters,  and  as  a  product 
of  the  decay  of  sulphur-containing  organic  substances.  It 
is  formed  by  direct  union  of  hydrogen  and  sulphur  vapor, 
and  by  the  action  of  nascent  hydrogen  from  acid  and 
metal  on  finely  divided  sulphur  suspended  in  water  (Schiit- 
zenberger) ;  also  by  the  action  of  acids  on  metallic  sulphides 
such  as  those  of  iron  and  zinc ;  or,  in  purer  condition,  from 
antimony  sulphide,  Sb2S3,  and  hydrochloric  acid.  The  ac- 
tion on  sulphides  is  the  common  laboratory  method  of 
supply. 

Hydrogen  sulphide  is  a  gas  without  color,  but  with  a  511 
marked  odor,  usually  described  as  that  of  rotten  eggs. 
The  substance  of  the  egg,  since  it  contains  sulphur,  pro- 
duces hydrogen  sulphide  in  putrefying.  The  gas  is  con- 
densable to  a  liquid  which  boils  at  —  62°  and  fieezes  at 
—  85°.  One  volume  of  water  dissolves  about  3.5  volumes 
of  the  gas  at  ordinary  temperature.  The  solution  reddens 
litmus  and  slowly  decomposes,  precipitating  sulphur.  The 
gas,  too,  is  separated  into  hydrogen  and  sulphur  by  heating 
to  400°.  It  is  combustible,  and  with  air  may  make  an  ex- 
plosive mixture.  It  is  extremely  poisonous  to  inhale.  Ex- 
posure to  air  containing  even  a  small  quantity  of  it  is 
likely  to  produce  headache.  It  reacts  with  many  metals 
and  with  their  salts  in  solution,  producing  metallic  sul- 


190        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

phides,  and  in  this  way  is  much  used  as  a  laboratory  reagent. 

512  The  metallic  sulphides  are  salts  of  this  acid,  although  made 
also  by  direct  union  of  metal  and  sulphur.     The  gas,  its 
water  solution,  and  the  sulphides  show  a  marked  tendency 
to  combine  with  oxygen ;  they  act,  therefore,  as  reducing 
agents.     A  hydrogen  persulphide  of  undetermined  compo- 
sition, H2S1+,  and  many  metallic  per  sulphides — e.  g.,  CaS2 
— are  known.     Such  persulphides,  when  decomposed  by  an 
acid,  generally  yield  hydrogen  sulphide  and  sulphur. 

513  Of  sulphur  chlorides,  there  are  known  S2C12,SC12,  and  SC14. 
The  first  is  a  fuming  liquid,  made  by  direct  action  of  chlor- 
ine gas  on  melted  sulphur.     It  finds  some  industrial  use— 
e.  g.,  in  refining  sugar,  and  in  making  India-rubber  goods. 

14b.  The  Oxides  of  Sulphur,  and  the  Acids  of  Sulphur 
containing  Oxygen 

514  Of  these  substances  the  following  are  known  : 

(1)  The  sesquioxide,  S203. 

(2)  The  dioxide,  S02. 

(3)  The  trioxide,  S03. 

(4)  The  peroxide,  S207. 

Hyposulphurous  acid,  H2S02  (?). 

(2)  Sulphurous  acid,  H2S03. 

(3)  Sulphuric  acid,  H2S04. 
Thiosulphuric  acid,  H2S203. 
Pyrosulphuric  acid,  ^I2S207. 

(4)  Per  sulphuric  acid,  H2S208. 

The  oxides  2,  3,  and  4  with  water  form  the  acids  which 
are  correspondingly  numbered.  Of  these,  only  the  second 
and  third  need  be  considered. 

515  Sulphur  dioxide  (S02). — This  is  formed  by  the  burning 
of  sulphur  and  of  substances  containing  unoxidized  sul- 
phur, and  by  the  action  of  hydrochloric  or  other  acid  on 
sulphites;  also  by  the  removal  of~6xygen  from  sulphuric 


DESCRIPTION  OF   ELEMENTS  AND  COMPOUNDS    191 

acid,  H2OS03i     These  methods  are  sufficiently  explained 
by  the  following  equations  : 


2HC1  =  S03  +  H20 
C  +  2H2S04  =  2S02  +  C02  +  2H20. 
S  +  2H2S04  =  3S02  +  2H20. 
Cu  +  2H2S04  =  S02  +  2H20  +  CuS04. 

Sulphur  dioxide  is  at  ordinary  temperature  a  gas  with-  516 
out  color,  but  with  marked  odor,  and  is  extremely  irritating 
to  inhale.  Its  specific  gravity  is  31.97  (H  =  1)  or  2.2  (air 
=  1).  In  liquid  form  it  boils  at  —8°  and  freezes  at  —76°. 
One  volume  of  water  dissolves  about  40  volumes  of  the 
gas  at  ordinary  temperature,  and  loses  it  by  boiling.  The 
solution  reddens  litmus  and  contains  sulphurous  acid, 
H2S03.  The  gas  is  not  combustible,  nor  does  it  support 
ordinary  combustion,  although  finely  divided  iron,  tin,  and 
potassium  burn  in  it,  forming  both  oxide  and.  sulphide.  It 
combines  directly  with  oxygen  to  form  the  trioxide.  It 
acts  upon  many  coloring  substances  in  the  presence  of 
water,  destroying  the  color,  and  is  used  largely  as  a  bleacher. 
In  some  cases  the  color  is  restored  by  time  and  by  treat- 
ment with  dilute  acid  or  alkali.  It  is  also  an  effective  anti- 
septic, being  used  in  preserving  meat  ;  and  as  a  disinfectant 
and  germicide  it  is  used  in  fumigating  clothing  and  habi- 
tations to  prevent  the  spread  of  disease.  It  is  also  used  in 
paper-making,  tanning,  and  in  refining  sugar.  The  liquid 
substance  is  supplied  in  commerce  to  some  extent. 

The  sulphites  are  both  normal  and  acid  —  e.  g.,  Na2S03  517 
and  NaHS03  ;  and,  like  the  acid  and  the  gas,  they  act  as 
reducing  agents,  by  virtue  of  the  tendency  to  form  the  tri- 
oxide, S03,  and  its  compounds. 

Sulphur  trioxide,  —  This  oxide  is  formed  when  a  mixture  513 
of  the  dioxide  and  oxygen  is  passed  over  hot  platinum  or 
other  substances  which  favor  oxidation.     It  is  also  formed 
to  some  extent  when  sulphur  is  burned  in  oxygen.     From 


192        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

sulphuric  acid,  H2OS03,  it  is  obtained  by  the  dehydrating 
action  of  phosphorus  pentoxide,  and  from  the  pyrosulphuric 
acid,  H2S04-S03,  or  pyrosulphates  simply  by  heating.  It  is 
a  white  crystalline  solid  which  melts  at  15°  and  boils  at  46°. 
It  fumes  strongly  when  exposed  to  moist  air,  since  its  vapor, 
combining  with  moisture,  produces  the  less  volatile  sul- 
phuric acid.  When  the  solid  comes  in  contact  with  water, 
combination  takes  place  with  great  energy.  It  is  capable 
even  of  removing  the  constituents  of  water  from  many 
things— e.  g.,  wood,  paper,  and  the  skin — and  therefore  it 
chars  them  as  fire  does.  It  combines  directly  with  some 
metallic  oxides  forming  sulphates — e.  g.,  BaOS03.  It  is 
decomposed  at  red  heat  into  the  dioxide  and  oxygen.  It 
has  some  industrial  use,  particularly  in  making  dye-stuffs. 

519  Sulphuric  acid,   H2OS03,  or  H2S04,  is  formed  by  the 
oxidation  of  sulphurous  acid  and  by  the  direct  combination 
of  the  trioxide  with  water.     The  substance  whose  composi- 
tion is  exactly  represented  by  H2OS03  is  called  monohy- 
drated  sulphuric  acid.     It  is  a  colorless  dense  oily  liquid, 
of  the  specific  gravity  1.85.     It  easily  solidifies  to  crystals 
which  melt  at  10.5°.     When  boiled,  it  gives  off  the  trioxide 
until  the  temperature  reaches  338°,  when  the  latter  remains 
constant,  and  an  acid  containing  98.5  per  cent  of  H2S04 
passes  over  continuously.     And  dilute  solutions  of  the  acid 
by  boiling  lose  water  and  become  concentrated  until  a  liquid 
of  this  same  composition  is  reached,  when  the  liquid  itself 
passes  over,  giving  the  same  distillate  of  98.5  per  cent  acid. 

The  monohydrated  acid  still  combines  with  water  very 
energetically,  even  removing  it,  like  the  trioxide,  from  other 
substances  and  charring  them.  The  maximum  of  heat  is 
liberated  when  the  ratio  of  acid  to  water  is  represented 
by  H2S04  +  2H20.  The  hydrate,  H2S04-H20,  has  been  ob- 
tained in  crystals  melting  at  8°  ;  and  another,  H2S04'4H20, 
which  melts  at  —25°.  Pyrosulphuric  acid,  H2S04-S03,  or 
H2O2S03,  is  known  also  as  fuming  or  Nordhausen  sulphu- 

520  ric  acid.    It  is  made  by  dissolving  the  trioxide  in  the  ordi- 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    193 

nary  acid,  and,  commercially,  by  decomposing  crystallized 
iron  sulphate  at  high  temperature,  as  thus  expressed : 

2FeS04-H20  =  Fe203  +  S03  +  S03  +  2H20. 

The  acid,  H2S04-S03,  has   the   specific  gravity  1.88  and 
melts  at  35°. 

The  ordinary  sulphates  are  salts  of  the  monohydrated  521 
acid,  H2S04,  but  salts  corresponding  to  the  other  hydrates 
are  known.  The  former  are  among  the  most  common  and 
important  of  all  salts.  They  are  of  two  types,  the  normal 
and  the  acid  salts — e.  g.,  sodium  sulphate,  Na2S04,  and 
sodium  acid  sulphate,  NaHS04. 

The  thiosulphates  are  salts  of  thiosulphuric  acid,  H2S203.   522 
The  most  common  one  is  the  sodium  salt,  Na2S203,  which 
is  used  in  photography  as  a  solvent  for  silver  chloride  and 
bromide.     It  is  more  familiarly  known  under  the  incorrect 
name  of  sodium  hyposulphite. 

14c.  The  Manufacture  of  Sulphuric  Acid 

The  first  record  of  making  sulphuric  acid  is  that  of  Valentine  in  523 
the  last  half  of  the  fifteenth  century,  although  the  substance  was  known 
as  early  as  the  tenth  century.  His  method  was  by  heating  green  vitriol 
(iron  sulphate),  and  the  substance  was  called  "  oil  of  vitriol,"  or  "  vitrj- 
olic  acid."  The  former  name  is  still  used  somewhat  in  commerce. 
About  1740  the  method  of  burning  sulphur  in  connection  with  potas- 
sium nitrate  was  used  on  a  small  scale  by  Ward  in  England,  and  this 
has  developed  into  one  of  the  most  important  and  extensive  of  the  in- 
dustries based  upon  chemical  processes ;.  the  product  is  consumed  in 
great  quantity  and  for  a  great  variety  of  purposes.  The  method  of 
making  consists  essentially  of  three  steps :  First,  producing  sulphur  di- 
oxide by  burning  sulphur ;  second,  changing  this  by  means  of  nitrogen 
oxides  to  sulphur  trioxide,  and  combining  the  latter  with  water;  third, 
concentrating  and  purifying  the  product. 

1.  The  crude  material  for  making  the  dioxide  is  preferably  sulphur,    524 
but  the  cheaper  iron  pyrites  (FeS2),  when  it  contains  as  much  as  35  per 
cent  of  sulphur  and  also  other  sulphides,  are  largely  used  for  the  im- 
purer  grades  of  acid.    Arsenic  coming  from  the  pyrites  is  often  an  im- 
purity of  this  product.    The  combustion  is  accomplished  in  furnaces 


194        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

with  a  carefully  regulated  supply  of  air,  and  generally  without  other 
fuel  than  the  sulphur  itself. 

525  *  2.  In  connection  with  the  furnace  are  placed  the  "  niter  pots,"  into 
which  is  placed  a  mixture  of  sodium  nitrate  and  sulphuric  acid  in  such 
proportion  as  to  form  the  acid  sulphate,  NaHS04 ,  and  liberate  the  nitric 
acid.     The  hot  gases  from  the  furnace  volatilize  the  nitric  acid,  which, 
mixing  with  the  dioxide  and  steam,  gives  rise  to  reactions  which  may 
in  their  general  character  be  represented  by  one  or  both  of  the  fol- 
lowing equations : 

2SOa  +  2HNO,  +  HaO  =  2HaS04  +  N203 . 

3SOa  +  2HNO,  +  2HaO  =  3HaS04  +  2NO. 

The  mixed  gases  .are  carried  into  large  chambers  lined  with  sheet 
lead,  and  into  these  steam  is  injected.  The  exact  nature  of  the  reac- 
tions taking  place  is  much  disputed.  They  are  undoubtedly  compli- 
cated, but  the  result  is  simple  enough.  The  nitric  oxide  is  reoxidized 
to  the  higher  oxide  by  contact  with  the  oxygen  of  the  air ;  this  in  turn 
gives  up  oxygen  to  more  sulphur  dioxide,  is  reduced,  again  oxidized, 
and  so  on  indefinitely.  Thus  a  comparatively  small  quantity  of  nitro- 
gen oxide  acts  as  carrier  of  a  large  quantity  of  oxygen  from  the  air 
to  the  sulphur  dioxide.  The  sulphuric  acid  forms  as  a  mist  in  the 
chambers,  which  settles  to  the  floor  and  is  drawn  off  as  a  liquid  con- 
taining about  68  per  cent  of  sulphuric  acid.  To  prevent  the  waste  of 
nitrous  fumes,  the  gases  at  their  exit  from  the  series  of  chambers  are 
passed  from  the  bottom  to  the  top  of  a  tower,  which  is  loosely  filled  with 
lumps  of  coke.  Over  these,  trickles  sulphuric  acid,  somewhat  more  con- 
centrated than  that  of  the  chambers.  This  acid  dissolves  the  nitrogen 
oxides,  forming  an  unstable  compound,  and  the  liquid  is  conducted 
from  the  base  of  this  tower  to  the  top  of  another  similar  one.  In  its 
passage  down  the  latter  it  is  brought  in  contact  with  the  hot  mixed 
gases  coming  from  the  furnace  and  on  their  way  to  the  chambers.  Un- 
der these  conditions  the  nitrogen  oxides  are  given  up,  and  contribute  to 
the  oxidation  of  the  sulphur,  dioxide.  There  is  some  loss  of  nitrogen 
oxides  through  imperfect  absorption  in  the  tower,  as  well  as  by  second- 
ary reactions  in  the  chambers. 

526  3.  The  product  is  further  concentrated  by  heating  in  glass  or  plati- 
num retorts  until  acid  of  93  or  95  per  cent  is  obtained  (oil  of  vitriol), 
although  the  process  may  be  carried  on  until  98  per  cent  is  reached. 
By  cooling  such  acid  to  —20°,  it  crystallizes;  the  crystals  are  sepa- 
rated and  drained  by  pressure,  then  melted,  and  an  acid  of  100  per  cent 
is  obtained.    Commercial  acid  is  likely  to  contain  lead  sulphate  in  solu- 
tion, which  is  precipitated  when  the  acid  is  diluted.     It  is  purified  by 
redistillation, 


V 

DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    195 

15.  CHLORINE 

Cl.— 35.18 

History. — The  substance  now  known  as  chlorine  was  first  obtained   52  7 
by  Scheele  in  1774  from  hydrochloric  acid  and  manganese  dioxide,  but 
it  was  regarded  as  a  compound  until  Davy  in  1810  proved  it  to  be  an 
element,  and  suggested  its  name,  signifying  greenish-yellow. 

Natural  occurrence. — It  is  not  found  free,  but  as  a  con-  528 
stituent  it  is  abundant  in  many  native  chlorides.     In  so- 
dium and  potassium  chlorides  it  comes  into  important  rela- 
tion with  the  plant  and  animal  organism. 

Preparation. — The  purely  chemical  methods  of  making  529 
chlorine  obtain  it  from  hydrochloric  acid  by  oxidizing  the 
hydrogen  to  water  and  thus  liberating  the  chlorine.  The 
methods  differ  chiefly  as  to  the  means  of  effecting  the 
oxidation.  The  hydrochloric  acid  itself  must  come  from 
a  native  chloride,  commonly  that  of  sodium.  It  will  be 
recalled  that  this  acid  is  a  by-product  in  the  Leblanc  soda 
process,  therefore  the  chlorine  manufacture  is  usually  asso- 
ciated with  the  former.  As  oxidizing  material,  potassium 
chlorate,  KC103,  red  lead,  Pb304,  potassium  dichromate, 
K2Cr207,  manganese  dioxide,  Mn02,  and  the  oxygen  of  the  air 
are  used.  In  the  laboratory,  potassium  chlorate  and  man- 
ganese dioxide  are  the  most  convenient.  When  the  former  529/1 
is  used  the  general  character  of  the  reaction  may  be  seen 
in  the  following  equation  : 

KC103  +  6HC1  =  KC1  +  3H20  +  6C1. 

When  the  latter  is  used  the  final  result  is  such  as  indicated 
by  the  equation : 

Mn02  +  4HC1  =  Mn013  +  2H20  +  2C1. 

This  result  is  in  consequence  of  the  fact  that  the  only 
stable  chloride  of  manganese  is  the  one  corresponding  to 
manganous  oxide,  MnO,  which  with  hydrochloric  acid  forms 
manganous  chloride,  Mn012,  and  water,  with  no  liberation 
14 


ft 
196        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

of  chlorine.  Any  higher  oxide,  therefore,  yields  an  excess 
of  oxygen  which  is  capable  of  oxidizing  the  hydrogen  of 
the  acid.  In  order  to  liberate  chlorine,  the  mixture  of  acid 
and  oxide  is  heated,  by  which  any  higher  chloride,  if  tem- 
porarily formed,  as  has  been  thought,  is  broken  up  into 
the  dichloride  and  chlorine.  The  manufacture  of  chlorine 
on  the  commercial  scale  will  be  described  in  a  later  section. 

530  Properties. — Chlorine  is  a  greenish-yellow  gas  of  peculiar 
and  disagreeable  odor,  intensely  irritating,  and  poisonous  if 
inhaled  in  quantity.     It  is  about  2.5  times  heavier  than 
air,  and  condenses  to  a  liquid  which  boils  at  —33.6°  and 
freezes  at  —102°.     One  volume  of  water  dissolves  about  2.2 
volumes  of  the  gas  in  ordinary  conditions.     The  water  solu- 
tion is  not  stable,  for  hydrochloric  acid  is  slowly  formed 
and  oxygen  liberated.     When  the  solution  is  cooled  nearly 
to  0°,    a   crystallized   hydrate,  C1-5H20,  separates.     It  is 
much  less  soluble  in  a  solution  of  sodium  chloride  than  in 
pure  water. 

531  Chlorine  is  markedly  reactive,  but  less  so  than  fluorine. 
It  does  not  burn  in  air,  although  compounds  with  oxygen 
exist.     In  an  atmosphere  of  hydrogen  it  burns  readily,  and 
a  mixture  with  hydrogen  in  equal  volumes  ignites  explo- 
sively ;  indeed,  a  ray  of  sunlight  or  of  magnesium  light  is 
sufficient  to  provoke  explosive  combination  in  the  mixture. 
The  product  in. all  cases  is  hydrochloric  acid.     Chlorine 
removes  hydrogen  from  other  substances  besides  water,  espe- 
cially from  organic  substances ;  in  consequence  a  lighted 
candle  continues  to  burn  in  chlorine  gas,  for  the  material 
of  the  candle  contains  carbon  and  hydrogen ;  with  the  latter 
the  chlorine  combines,  and  the  carbon  is  seen  in  the  dense 
black  smoke.     Some  such  organic  substances — e.  g.,  tur- 
pentine— inflame  spontaneously  in  chlorine  gas.     For  the 
same  reason  chlorine  acts  as  a  powerful  bleacher,  often 
destroying  the   coloring   substance.     Under   some   condi- 
tions the  chlorine  not  only  removes  hydrogen  from  a  com- 
pound, but  in    addition   takes   its   place  as    constituent 


DESCRIPTION  OF   ELEMENTS  AND  COMPOUNDS    197 

(substitution).     This  is   illustrated  in   the   reaction  with 
benzene,  C6H6,  thus : 

C6H6  +  201  =  C6H5C1  +  HC1. 

Associated  with  water,  chlorine  is  an  active  oxidizing  532 
agent,  for  it  combines  with  the  hydrogen  and  liberates 
nascent  oxygen.  For  this  purpose  it  is  often  used  in  the 
laboratory ;  thus  chlorine  water  with  hydrogen  sulphide  lib- 
erates sulphur.  These  properties  make  it  useful  as  a  disin- 
fectant and  deodorizer.  It  combines  directly,  especially 
when  moist,  with  most  of  the  metals,  and  also  with  phos- 
phorus, so  that  compounds  exist  with  all  the  elements  pre- 
ceding it  in  the  list,  except  fluorine. 

Hydrochloric  acid. — This  substance,  or  its  water  solution,  533 
was  known  as  early  as  the  fifteenth  century,  perhaps  earlier, 
but  Davy,  in  1810,  first  proved  that  it  contained  only 
chlorine  and  hydrogen.  It  occurs  free  in  some  volcanic 
gases  and  in  some  natural  waters.  The  native  chlorides, 
as  well  as  the  preparation  of  the  acid,  have  already  been 
sufficiently  considered.  The  anhydrous  hydrogen  chloride  534 
is  a  colorless  gas  very  irritating  to  inhale,  and  about  1.25 
times  heavier  than  air.  Its  boiling  point  is  —102°,  and 
freezing  point  —112.5°.  It  does'  not  burn  nor  support  com- 
bustion. It  has  strong  tendency  to  dissolve  in  water,  and 
probably  to  combine  with  it,  so  that  the  gas  itself,  or  the 
vapor  from  a  strong  solution  of  it,  fumes — that  is,  forms  a 
mist  or  cloud  when  in  contact  with  moist  air ;  this  may  be 
due  to  the  formation  of  a  less  volatile  hydrate.  The  gas  is 
extremely  soluble  in  water,  one  volume  of  the  latter  dis- 
solving about  450  volumes  of  the  gas  at  18°  and  ordinary 
pressure.  The  Solution  has  the  specific  gravity  1.2  and 
contains  42  per  cent  by  weight  of  the  anhydrous  substance. 
When  a  solution  is  heated  it  loses  water  or  acid,  as  the  case 
may  be,  until  the  mixture  has  a  specific  gravity  of  1.1  and 
contains  20  per  cent  of  acid,  and  boils  at  110°  at  ordinary 
pressure,  when  the  solution  distills  without  change.  A 


198        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

crystallized  hydrate,  HC1-2H20,  separates  on  cooling  a  satu- 
rated solution  to  —18°. 

535  The  commercial  article,  often  designated  as  muriatic 
acid,  is  a  water  solution  containing  about  40  per  cent  by 
weight  of  the  hydrogen  chloride.     Various  impurities  are 
present,  often  sulphuric  acid,  and  iron  and  calcium  chlo- 
rides, and  it  is  more  or  less  yellow  in  consequence.     The 
purified  acid  is  colorless. 

Hydrochloric  acid  is  consumed  in  large  quantity,  chiefly 
in  making  chlorine,  but  also  in  making  metallic  chlorides 
and  carbon  dioxide,  and  for  various  minor  purposes. 

536  15a.     The  Oxides  of  Chlorine  and  their  Acids 
Of  these  compounds  the  following  are  known : 

Oxides.  Acids. 

C120.  HC10,  hypochlorous  acid. 

(C1202)  unknown.  No  acid. 

(C1203)  unknown.  HC102,  chlorous  acid. 

CIO*  No  acid. 

(C1205)  unknown.  HC103,  chloric  acid. 

(C1207)  unknown.  HC104,  perchloric  acid. 

Chlorine  and  oxygen  do  not  combine  directly. 

537  The  monoxide,  C120,  is  formed  by  reaction  between  dry 
chlorine  and  mercuric  oxide  at  ordinary  temperature  : 

2HgO  +  4C1  =  HgO-HgCl2  +  C120. 

It  is  a  yellow  gas,  of  odor  somewhat  like  that  of  chlorine, 
and  condensable  to  a  liquid  which  boils  at  —20°.  The  for- 
mation heat  of  the  gas  is  —17,800  calories,  and  both  gas 
and  liquid  are  violently  explosive  on  very  slight  provoca- 
tion. One  volume  of  water  dissolves  about  100  volumes  of 
the  gas  and  hypochlorous  acid,  HC10,  is  produced.  The 

538  acid  solution  also  is  unstable  and  can  not  be  concentrated. 
It  is  a  very  active  oxidizing  and  bleaching  substance,  readily 
splitting  into  hydrochloric  acid  and  oxygen.     With  hydro- 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    199 

chloric  acid,  water  and  chlorine  are  formed.     Its  salts,  the 
hypochlorites,  are  more  stable,  but  are  decomposed  by  car- 
bonic acid.     When  an  alkali  hydroxide  in  solution  is  treated  539 
with  chlorine  in  the  cold,  both-  chloride  and  hypochlorite 
are  formed,  thus  : 

SNaOH  +  2C1  =  NaCl  +  NaCIO  +  H20. 

The  same  formation  takes  place  with  solution  of  sodium 
carbonate.  With  calcium  hydroxide  (limewater),  the  reac- 
tion is — 

2Ca(OH)2  +  4C1  =  CaCl2  +  Ca(C10)2  +  2H20. 

If  excess  of  chlorine  is  present,  the  hypochlorous  acid  is 
liberated.  Such  solutions,  made  by  treating  with  chlorine 
the  hydroxide,  or  the  carbonate,  of  sodium,  or  of  potassium, 
or  of  calcium,  are  active  oxidizers  and  bleachers,  and  have 
been  much  used  for  these  purposes.  The  calcium  hypo- 
chlorite has  been  obtained  in  crystallized  condition.  In 
the  presence  of  small  quantities  of  some  substances — e.  g., 
cobalt  salt — hypochlorite,  like  the  free  acid,  liberates  oxygen: 

Ca(C10)8=CaCl8  +  20. 

The  peroxide. — This  is  the  name  generally  given  to  the  540 
substance  C102.     It  is  formed,  along  with  perchlorate,  by 
the  action  of  sulphuric  acid  on  potassium  chlorate  : 

3KC108  +  2H2S04  =  2KIIS04  +  KC104  +  H20  +  2C102 ; 

also  by  the  action  of  a  feeble  reducing  substance  on  chloric 
acid,  HC103.  It  is  a  dark-red  liquid  which  boils  at  9° ;  the 
gas  is  dark  yellow,  and  has  a  specific  gravity  which  indi-  • 
cates  the  formula  C102.  It  dissolves  in  water  abundantly, 
probably  forming  chlorous  acid,  HC102,  and  chloric  acid, 
HC103.  This  oxide,  like  the  preceding,  is  very  unstable, 
decomposing  explosively,  particularly  if  brought  in  contact 
with  oxidizable  matter.  Some  substances,  like  phosphorus 
and  hydrogen  sulphide,  take  fire  in  the  gas  at  ordinary 
temperature. 


200        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

541  Of  chlorous  acid,  HC102,  and  the  chlorites,  nothing  fur- 
ther need  be  said.  Chloric  acid,  HC103,  and  perchloric 
acid,  HC104,  are  likewise  explosively  unstable  and  very 
energetic  oxidizers.  Their  salts  are  more  stable  than  the 
free  acids.  Potassium  and  sodium  chlorates  have  some 
industrial  importance.  They  are  formed  by  boiling  the 
solutions  of  the  hypochlorites,  thus  : 

3KC10  =  KC103  +  2KC1. 

Or,  if  chlorine  is  passed  into  hot  solution  of  the  hydroxide, 
this  reaction  takes  place  : 

6KOH  +  6C1  =  5KC1  +  KC103  +  3H20. 

The  chlorate  is  less  soluble  than  the  chloride,  and  is  sepa- 
rated by  crystallization.  Practically,  however,  calcium 
chlorate  is  first  produced  by  the  action  of  chlorine  on  milk 
of  lime,  Ca(OH)2,  whereby  the  hypochlorite  is  formed. 
This,  by  heating  with  excess  of  chlorine,  is  converted  into 
chlorate  and  chloride.  Finally  potassium  chloride  is  added, 
and  potassium  chlorate  crystallizes  out  on  concentration. 
This  substance  is  used  in  making  oxygen  gas,  matches,  fire- 
works, fuses,  and  some  kinds  of  gunpowder  and  other  explo- 
sives, and  as  oxidizer  in  the  preparation  of  some  of  the  dye- 
stuffs.  It  is  also  used  to  some  extent  in  medicine. 

15b.     Bromine  and  Iodine 

Br.— 79.35.     I.— 125.9 

541/1  There  is  convenience  of  arrangement  in  briefly  describ- 
ing at  this  point  the  elements,  bromine  and  iodine,  Nos. 
32  and  47  in  the  list.  They  are  very  similar  to  chlorine 
and  fluorine.  Neither  is  found  free,  but  both  occur  native 
as  constituents,  chiefly  in  the  bromides  and  the  iodides 
respectively..  Of  these  the  sodium,  potassium,  calcium, 
and  magnesium  salts  are  the  most  common,  occurring  in 
sea  water,  in  some  mineral  waters,  and  in  sea  plants.  The 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    201 

ashes  of  the  latter  are  a  commercial  source.  Their  prepa- 
ration is  similar  to  that  of  chlorine.  It  consists  in  the 
liberation  from  bromides  and  iodides  by  the  action  of 
sulphuric  acid  and  an  oxidizing  substance  (e.  g.,  Mn02), 
and  the  subsequent  purification  by  distillation.  Bromine 
is  a  very  volatile  liquid,  boiling  point  59°,  and  iodine  is  a 
solid,  melting  point  114°  and  boiling  point  184°.  Bromine 
is  of  a  dark  red-brown  color  both  as  liquid  and  as  vapor. 
Iodine  is  lustrous  and  almost  black,  and  highly  crystalline. 
It  readily  sublimes,  and  the  vapor  is  reddish-violet.  Both 
have  marked  odor,  that  of  the  former  being  especially  dis- 
agreeable (hence  its  name  signifying  stench).  Both  dis- 
solve readily  in  carbon  disulphide  and  in  some  other  sol- 
vents. Bromine  is  only  slightly  soluble  in  water,  and  iodine 
is  still  less  so.  Both  are  highly  reactive,  corrosive,  and  poi- 
sonous, the  former  more  than  the  latter.  Bromine  displaces 
iodine  in  combination,  and  both  are  displaced  by  chlorine. 
They  form  compounds  with  most  of  the  other  elements, 
combining  with  many  of  them  directly.  No  oxide  of  bro- 
mine has  been  obtained  free,  although  it  exists  as  a  con- 
stituent. Of  iodine  the  pentoxide,  I205,  is  the  only  oxide 
whose  existence  in  the  free  condition  is  known.  They 
combine  with  hydrogen,  less  readily  in  the  case  of  iodine, 
and  the  products  are  hydracids — viz.,  hydrobromic  acid, 
HBr,  and  hydriodic  acid,  HI.  The  sodium  and  potassium 
salts  of  these  are  the  most  common.  Bromic  acid,  HBr03, 
and  iodic  acid,  HI03,  and  their  salts  are  known,  and  hypo- 
bromites  and  hypoiodites  probably  exist,  but  are  less  stable 
than  the  hypochlorites.  The  four  elements  fluorine,  chlo-  - 
rine,  bromine,  and  iodine  are  often  called  the  halogens. 

15c.  The  Manufacture  of  Chlorine  and  of  Bleaching  Powder 

Chlorine  has  considerable  industrial  use.    Its  applicability  to  bleach-    542 
ing  was  suggested  as  early  as  1785  by  Berthollet,  and  in  1789  the 
bleaching  liquor  known  as  "  eau  de  Javel "  was  manufactured.     This 
was  practically  a  solution  of  potassium  hypochlorite,  and  it  made  a 


202        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

more  available  commercial  article  than  the  gaseous  chlorine.  In  1798 
the  cheaper  material,  lime,  was  used  to  prepare  a  similar  liquor,  which 
is  still  somewhat  used.  The  use  of  dry  calcium  hydroxide,  and  the 
preparation  of  a  "  bleaching  powder,"  was  accomplished  in  1799.  This 
has  the  advantage  of  greater  stability,  although  the  material  which 
is  in  the  form  of  solution  is  more  convenient,  more  concentrated,  and 
cheaper.  Quite  recently  chlorine  itself  in  liquid  condition,  stored  under 
pressure  in  steel  cylinders,  has  come  into  commerce. 

543  For  making  the  chlorine,  the  reaction  with  manganese  dioxide  is 
largely  used.     The  crude  ore  is  pyrolusite,  which  may  contain  from  70 
to  85  per  cent  of  the  dioxide,  MnOa.     Sometimes  a  mixture  of  common 
salt  and  the  dioxide  is  acted  upon  by  sulphuric  acid,  but  more  com- 
monly the  hydrochloric  acid  from  the  Leblanc  process  is  applied  di- 
rectly to  the  dioxide.     The  operation  is  carried  on  sometimes  in  stone- 
ware retorts,  heated  from  without  by  hot  water ;  sometimes  in  vessels 
built  of  stone  slabs,  into  which  steam  is  introduced  for  the  necessary 
heating.     The  ore  is  used  in  coarse  lumps,  and  is  often  contained  in  a 
sievelike  vessel,  or  spread  on  a  perforated  raised  bottom  of  the  tank. 
The  hydrochloric  acid  is  admitted  gradually.     When  the  reaction  is 
over,  the  liquid  left  in  the  generator,  called  the  "  still-liquor,"  contains 
principally  manganese  dichloride,  MnCla,   with   considerable  unused 
hydrochloric  acid  and  some  iron  chloride,  and  it  is  still  capable  of  lib- 
erating some  chlorine.     This  was  at  one  time  allowed  to  go  to  waste, 
but  as  it  must  necessarily  be  a  great  nuisance,  the  disposal  of  it  became 
a  problem.     It  was  finally  discovered  that  from  this  material  the  man- 
ganese could  be  recovered  and  used  over  again.    One  method  of  accom- 
plishing this  was  first  brought  into  practical  use  in  1869,  and  is  known 
as  the  Weldon  process. 

544  The  Weldon  process,  so  far  as  pertains  to  the  chemical  reactions,  is 
as  follows :  The  "  still-liquor "  is  mixed  with  powdered  limestone  or 
chalk,  CaCOs,  whereby  the  free  acid  is  neutralized  and  the  iron  is  pre- 
cipitated.    The  precipitate  is  allowed  to  settle,  and  the  clear  solution 
of  manganese  and  calcium  chlorides  is  drawn  off.     To  this  solution  is 
added  milk  of  lime,  until  the  manganese  is  all  precipitated  as  hy- 
droxide : 

MnCla  +  Ca(OH),  =  MnO-H30  +  CaCl,. 

Then  from  one  half  to  one  quarter  more  lime  is  added  for  excess,  and 
air,  somewhat  heated,  is  blown  into  the  pasty  mixture.  The  oxygen 
converts  the  manganese  monoxide  into  the  dioxide,  which,  acting  as  an 
acid,  combines  with  the  lime  as  a  base,  forming  principally  CaO.Mn09. 
The  mixture  is  still  in  the  form  of  a  thin  paste,  and  it  is  run  into  set- 
tling tanks,  where  the  clear  solution  of  calcium  chloride  separates  and 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    203 

is  drawn  off  as  waste.  The  manganese  compound  is  technically 
known  as  "  Weldon  mud,"  and  contains  about  80  per  cent  of  MnOa. 
It  is  run  directly  into  the  chlorine  generator,  to  be  treated  again 
with  hydrochloric  acid,  and,  being  very  finely  divided,  it  is  acted 
upon  quickly  and  completely.  The  loss  of  dioxide  is  only  2  or  3  per 
cent,  but  only  about  one  third  of  the  hydrochloric  acid  is  converted 
into  chlorine. 

The  Deacon  process  obtains  chlorine  from  hydrochloric  acid  by  the  545 
more  direct  action  of  oxygen  from  air.  When  a  mixture  of  the  two 
gases  is  heated,  chlorine  is  liberated,  but  only  slowly.  In  practice,  the 
hydrochloric  acid  and  air  are  heated  to  about  500°  and  passed  over 
bricks  which  have  been  wet  with  a  solution  of  copper  chloride,  CuCl2, 
the  presence  of  which  greatly  facilitates  the  liberation  of  chlorine,  prob- 
ably by  reason  of  the  alternate  formation  of  copper  oxide,  CuO,  and  the 
chloride.  From  the  resulting  mixture  of  gases,  the  hydrochloric  acid 
and  water  must  be  removed;  the  chlorine,  mixed  with  nitrogen  and 
oxygen,  is  then  available  for  use. 

Much  effort  is  being  expended  to  obtain  practicable  methods  of    546 
electrolyzing  the  solution  of  sodium  chloride,  as  a  means  of  producing 
both  sodium  hydroxide  and  chlorine,  but  the  problem  has  not  yet  been 
satisfactorily  solved. 

The  bleaching  powder,  or  "chloride  of  lime,"  is  produced  by  the  547 
action  of  chlorine  gas  on  slaked  lime,  Ca(OH)2.  The  latter  substance 
is  prepared  from  "  burned  lime,"  CaO,  by  adding  just  enough,  or  very 
slightly  more  than  enough,  water  to  form  the  hydroxide  and  to  leave 
it  in  the  condition  of  a  dry  powder,  which  is  carefully  sifted.  This  is 
spread  three  or  four  inches  deep  on  the  floor  of  a  chamber,  generally 
lead-lined,  and  chlorine  is  passed  in  so  long  as  the  powder  continues  to 
absorb  it.  The  product  is  a  powder,  nearly  white  in  color,  and  of 
peculiar  odor.  It  absorbs  moisture  and  carbon  dioxide  and  becomes 
pasty,  losing  at  the  same  time  some  of  its  chlorine,  and  consequently 
deteriorating.  It  must,  therefore,  be  packed  in  a  way  to  protect  it 
from  the  air,  and  from  light  which  hastens  decomposition.  It  is  largely 
used  to  bleach  materials  in  textile  and  paper-making  industries,  and  it 
is  one  of  the  best  disinfectants. 

There  has  been  much  discussion  as  to  the  exact  reaction  between    548 
the  dry  calcium  hydroxide  and  the  chlorine.     It  is  now  supposed  that 
a  substance,  CaOCl2,  is  formed  and  constitutes  the  bleaching  powder, 
but  is  converted  into  hypochlorite  when  brought  in  contact  with  water : 

2CaOCl2  =  Ca(C10)2  +  CaCl2. 
(Lunge-Thorpe  and  F.  H.  Thorp.) 


204        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 
16.   POTASSIUM 

K.— 38.82 

549  History. — The  element  potassium  was  obtained  first  by  Davy  in 
1807  by  the  electrolysis  of  the  hydroxide,  although  this  compound  and 
the  carbonate  had  been  known  from  the  early  days  of  alchemy. 

550  Natural  occurrence. — It  is  found  only  as  constituent,  but 
as  such  is  quite  abundant.      Its  silicate  is  contained  in 
granite,  sometimes  to  the  extent  of  3  per  cent,  and  also  in 
many  other  rocks.     The  chloride  and  sulphate  are  found 
in  large  deposits  in  the  neighborhood  of  Stassfurt.     These 
salts  are  present  also  in  sea  water  and  in  mineral  waters. 
The  occurrence  of  the  nitrate  (niter)  in  Chili  and  Peru  has 
been  mentioned  in  another  connection.     Potassium  com- 
pounds are  present  in  fertile  soils  and  are  important  in 
both  the  plant  and  the  animal  organism. 

551  The  preparation  of  potassium  by  the  reduction  of  its 
carbonate  and  of  its  hydroxide,  and  by  the  electrolysis  of 
its  hydroxide,  is  so  exactly  similar  to  that  of  sodium  that  it 
need  not  be  further  described.     (Compare  No.  409.) 

552  Properties. — Potassium,  like  sodium,  is  a  soft  white  metal. 
It  melts  at  62.5°  and  boils  at  667°,  a  little  lower  than  sodium. 
Its  specific  gravity  is  0.86.      It  oxidizes  in  moist  air  at 
ordinary  temperature,  and,  when  heated,  burns  energetic- 
ally.    To  the  Bunsen  flame  it  gives  a  violet  color,  as  do  its 
compounds.     It  decomposes  water  at  ordinary  temperature, 
and  carbon  dioxide,  when  heated ;  it  is,  therefore,  a  power- 

553  ful  reducing  agent.     As  to  oxides,  it  forms  at  least  K20  and 
K202.     The  hydroxide  is  KHO  ;  it  is  soluble  and  acts  as  a 
base,  forming  a  series  of  well  known  salts,  to  several  of 
which  reference  has  already  been  made.     The  chloride  is 
KC1,  and  the  nitrate  is  KN03,  niter  or  saltpeter.     The 

554  carbonate,  K2C03,  is   obtained  from   wood   ashes   and  is 
manufactured  from  the  chloride.     The  reactions  involved 
in  this,  as  well  as  in  making  the  hydroxide,  are  so  similar 
to  the  corresponding  ones  for  sodium,  that  they  need  not 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    205 

be  described.  (Compare  Nos.  414,  415,  and  419.)  The 
potassium  compounds  have  various  industrial  applications ; 
the  hydroxide  and  carbonate,  like  the  sodium  compounds, 
are  used  in  making  glass  and  soap ;  the  nitrate  is  largely 
used  as  a  constituent  of  gunpowder,  for  which  the  sodium 
nitrate,  owing  to  its  being  hygroscopic,  is  not  available. 


F.    GUNPOWDER  A^D  SOME  OTHER  EXPLOSIVES 

An  explosive  is  a  substance,  or  a  mixture  of  substances,  which  by  a  555 
chemical  change  quickly  generates  gaseous  products,  the  latter  at  the 
instant  of  their  formation  tending  to  occupy  a  much. greater  volume 
than  the  factors.  The  sudden  conversion  of  water  into  steam  may 
take  place  in  a  steam  boiler  and  cause  explosion,  but  no  chemical 
change  is  involved,  and  water  is  not  in  this  sense  called  an  explosive. 
On  the  other  hand,  liquid  acetylene  may  decompose  explosively  into 
carbon  and  hydrogen,  and  the  volume  of  the  hydrogen  gas  would  be 
very  much  greater  than  that  of  the  liquid  acetylene.  Furthermore, 
heat  is  liberated  by  the  decomposition,  and  hence  the  gas  would  be  con- 
siderably heated  and  tend  to  occupy  a  still  greater  volume.  So,  too,  a 
mixture  of  hydrogen  and  chlorine  explodes,  although  the  volume  of  the 
product  is  only  equal  to  that  of  the  factors ;  but  heat  is  liberated,  and 
so  the  temperature,  and  therefore  energy,  of  the  product  is  suddenly 
increased.  However,  all  the  explosives  in  practical  use  liberate  their 
energy  by  combustion ;  that  is  oxidation. 

Gunpowder  is  one  of  the  oldest  of  practical  explosives,  having  been  55(> 
used  for  firearms  as  early  as  1346.  It  is  a  mixture  of  potassium  nitrate, 
charcoal,  and  sulphur.  The  ingredients  are  carefully  purified,  finely 
ground,  and  very  thoroughly  mixed.  The  mixture,  slightly  damp,  is 
put  under  heavy  pressure — from  300  to  450  pounds  to  the  square  inch — 
in  order  to  increase  its  density.  The  "  press-cake  "  thus  obtained  is 
broken  into  small  grains — "  granulation  "  the  process  is  called — and 
sifted.  The  grains  are  smoothed  and  glazed  by  rolling  in  wooden 
drums,  sometimes  with  the  addition  of  a  little  graphite.  The  product 
is  again  sifted,  and  freed  of  moisture  by  drying  at  a  low  temperature. 
A  black  powder,  commonly  used  for  military  purposes,  contains  75  per 
cent  of  potassium  nitrate,  15  per  cent  of  charcoal,  and  10  per  cent  of 
sulphur.  Some  idea  of  the  chemical  change  in  the  explosion  is  given  55  7 
by  the  incomplete  equation  : 

2KN03  +  3C  +  S  =  3CO  +  2N  +  K2S  +  . 


206        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

But  it  is  actually,  at  least  when  taking  place  in  a  confined  Space, 
much  more  complicated.  However,  it  is  clear  that  the  carbon  and  the 
sulphur  may  be  converted  into  gaseous  oxides  by  the  oxygen  of  the 
nitrate,  and  thus  combustion  take  place  without  the  intervention  of 
air  to  any  extent.  The  large  volume  of  the  resulting  gases  and  the 
heat  liberated  by  the  reaction  cause  the  energy  of  the  explosion.  The 
gaseous  products  include : 

Carbon  dioxide,  C02 ; 
Nitrogen,  N ; 
Carbon  monoxide,  CO ; 
Hydrogen  sulphide,  H2S ; 
Hydrogen,  H ; 
Methane,  CH4. 

The  hydrogen  may  come  from  the  charcoal  or  from  the  moisture  pres- 
ent. Of  these  gases,  the  first  three  make  about  90  per  cent  of  the  total, 
while  somewhat  more  than  90  per  cent  of  the  total  solid  products  are 
made  up  of — 

Potassium  carbonate,  KaC08 ; 

Potassium  sulphate,  KaSO* ; 

Potassium  persulphide,  K2S2 . 

558  The  reaction  is  expressed  with  closer  approximation  by  the  equation, 

8KN03  +  9C  +  3S  =  2K2C03  +  K2S04  -f-  K2S2  +  7C02  -f  8N. 

From  1  gram  of  powder  the  solid  products  weigh  from  0.55  to  0.58 
of  a  gram,  and  the  gaseous  from  0.45  to  0.42  of  a  gram,  while  the  vol- 
ume of  the  gases  reckoned  at  0°  is  from  200  to  300  cubic  centimeters, 
and  the  temperature  is  estimated  at  2,100°  or  2,200°. 

559  It  is  evident  that  the  rending  effect  of  an  explosion  must  depend 
upon  the  rapidity  of  the  reaction,  for  if  the  latter  is  slow  the  gases  are 
slowly  liberated,  and  the  heat  is  gradually  dissipated,  so  that  the  tem- 
perature does  not  rise  as  high ;  moreover,  the  pressure  of  expansion, 
which  when  suddenly  applied  may  be  irresistible,  when  slowly  applied 
may  be  resisted.     Now,  if  the  reaction  is  one  of  oxidation  the  rapidity 
must  be  influenced  by  the  closeness  of  contact,  or  intimacy  of  mixture, 
of  the  combustible  with  the  supporter  of  combustion.     It  has  been 
seen  in  the  experiments  (see  Exp.  SSI/,)  that  a  piece  of  ignited  char- 
coal burns  actively,  but  not  explosively,  when  brought  in  contact  with 
melted  nitrate.     It  is  quite  different  if  the  two  substances  are  finely 
powdered  and  then   intimately  mixed,  as  in  gunpowder,  each  small 
grain  of  which  contains  its  proportion  of  the  three  ingredients.    Again, 
if  the  grains  are  made  larger  and  therefore  do  not  lie  so  closely  in  con- 


DESCRIPTION   OF  ELEMENTS  AND  COMPOUNDS    207 

tact,  the  rate  of  combustion  through  the  whole  mass,  when  the  ignition 
is  started  at  only  one  point,  must  be  retarded.  For  this  reason  the 
powder  used  in  heavy  guns,  known  as  "  pebble "  and  "  prismatic " 
powder,  is  made  into  grains  which  measure  from  five  eighths  to  one  and 
three  quarters  inches,  so  that  the  full  pressure  of  the  explosion  is  not 
reached  at  once.  Were  it  otherwise,  the  gun  might  yield  before  the 
ball  was  set  in  motion. 

Again,  the  velocity  of  combustion  through  a  mass  of  gunpowder  is  560 
influenced  by  the  pressure  of  surrounding  gases.  In  a  vacuum  it  does 
not  explode  at  all,  but  burns  slowly.  In  open  air  the  ignition  travels 
through  the  mass  at  the  rate  of  four  feet  per  second ;  in  a  heavy  gun  at 
about  thirteen  feet  per  second.  So  it  happens  sometimes,  in  using 
large-grained  powder,  that  the  charge  is  ignited  and  the  ball  leaves  the 
gun  before  combustion  reaches  the  last  of  the  powder,  and  this  is 
thrown  out  unburned.  Likewise  in  exploding  powder  under  water,  if 
the  containing  case  is  not  strong  enough  to  hold  the  gases  until  the 
ignition  is  complete,  a  part  of  the  charge  may  remain  unexploded 
(Walke).  By  varying  the  quality  of  the  charcoal,  a  "  brown "  or 
"  cocoa "  powder  is  made  which  is  so  slow  in  burning  that  a  large 
grain  may  be  ignited  while  held  in  the  hand  and  dropped  before  th'e 
fire  reaches  the  fingers. 

Still  again,  the  velocity  of  the  combustion  is  influenced  by  the  man-  561 
ner  of  firing.  In  the  foregoing  statements  it  has  been  implied  that  the 
chemical  reaction  which  produces  the  explosion  is  started  by  a  suffi- 
cient rise  of  temperature  in  only  a  small  portion  of  the  powder,  such  as 
is  practically  caused  by  a  spark  of  fire  or  a  wire  made  hot  by  the  electric 
current;  and  this  ignition,  producing  heat  and  flame,  spreads  with 
more  or  less  rapidity  through  the  whole.  But  there  is  another  mode  of  562 
firing,  known  as  detonation.  In  this  the  reaction  is  brought  about  by 
the  shock  of  another  explosion  and  can  not  be  due,  at  least  not  in  all 
cases,  to  rise  of  temperature.  A  very  common  detonating  material  is 
mercury  fulminate,  the  nature  of  which  need  not  be  explained  here. 
Its  application  is  seen  in  the  ordinary  percussion  cap  in  which  it  is 
exploded  by  a  blow,  although  when  this  is  used  in  connection  with 
powder  the  latter  is  probably  fired  by  the  small  flame  or  spark  from 
the  cap,  and  so,  strictly  speaking,  is  not  detonated.  However,  another 
explosive — namely,  gun  cotton — even  when  wet  may  be  exploded  by  the 
explosion  of  a  small  quantity  of  fulminate  in  contact  with  it.  In  this 
case  it  can  not  be  rise  of  temperature  which  explodes  the  gun  cotton. 
This  shock  of  detonation  is  brought  to  bear  upon  the  whole  mass  of 
the  explosive  within  the  reach  of  its  influence  instantaneously,  or  at 
least  with  a  rapidity  very  much  greater  than  the  velocity  of  ignition. 


208        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

It  is  as  if  a  violent  blow  were  given  to  every  minutest  particle  of  the 
explosive  at  practically  one  instant  of  time,  and  therefore  the  explosion 
is  made  more  violent.  Gunpowder  is  not  readily  detonated ;  indeed, 
this  method  of  explosion  is  not  desirable  for  firing  projectiles,  and  it  is 
somewhat  uncertain  whether  this  material  can  be  really  detonated  in 
any  conditions.  There  is  a  class  of  explosives  of  altogether  different 
chemical  character  which  are  most  readily  detonated.  Before  consider- 
ing these,  some  modification  in  the  constituents  of  gunpowder  may  be 
mentioned. 

563  The  nitrate  of  sodium,  because  of  its  cheapness,  is  substituted  for 
the  potassium  salt  in  mining  powder,  especially  when  it  is  to  be  used 
in  hot  and  dry  countries.     It  was  largely  employed  in  building  the 
Suez  Canal,  but  its  hygroscopic  quality  hinders  its  general  use.     The 
same  objection  applies  to  ammonium  nitrate,  although  it  has  the  advan- 
tage of  producing  a  larger  volume  of  gases  and  less  solids,  therefore 
less  smoke. 

564  Many  attempts  have  been  made  to  utilize  potassium  chlorate  as  oxi- 
dizing material.     This  decomposes  at  about  350°  into  potassium  chlo- 
ride and  oxygen,  with  liberation  of  heat.     A  chlorate  powder  produces 
higher  temperature  and  larger  volume  of  gas,  and  simpler,  less  disso- 
ciable products  ;  the  reaction  begins  at  lower  temperature  and  spreads 
with  greater  rapidity,  and  therefore  causes  more  abrupt  and  shattering 
effect  than  with  nitrate  powders.     But  the  former  are  much  more  sensi- 
tive, and  are  subject  even  to  (so-called)  spontaneous  explosion ;  therefore 
much  greater  danger  attends  their  preparation,  storage,  and  use.     Be- 
sides, the  products  of  decomposition  are  more  corrosive  of  the  gun  and 
more  injurious  to  the  person  than  with  the  nitrate  powders.    The  dis- 
advantages overbalance  the  advantages,  and  have  prevented  the  prac- 
tical success  of  powder  of  this  class  for  firing  projectiles.     But  mix- 
tures containing  chlorate  are  used  for  charging  explosive  shells  and 
bullets,  and  for  fuses  which  are  to  be  ignited  by  friction,  percussion,  or 
.contact;  in  them,  sugar  and  starch  are  sometimes  used  as  the  com- 
bustible material. 

565  Liquid  mixtures. — Some  attempts  have  been  made  to  use  liquid  mix- 
tures of  combustible  and  oxidizer,  in  which  evidently  the  contact  of 
the  two  would  be  more  intimate  than  in  the  mechanical  mixture  of 
powders.     One  such  mixture  consists  of  nitric  acid  as  oxidizer  and  sol- 
vent, and  certain  hydrocarbons  as  combustible.     They  seem  to  have  no 
practical  success. 

566  Gaseous  mixtures  must  bring  the  combustible  and  oxidizer  into  inti- 
macy of  the  same  order,  as  in  liquids,  reaching  to  the  minutest  par- 
ticles of  the  substances — that  is,  to  the  molecules  themselves.     But, 


DESCRIPTION   OF  ELEMENTS  AND  COMPOUNDS    209 

• 

from  the  very  nature  of  the  gaseous  condition,  it  would  seem  that  reac- 
tion by  shock  could  not  be  brought  about  as  in  liquids  and  solids,  and 
that  the  spread  of  the  combustion  must  depend  on  temperature  or  in- 
flammability. In  combustion  of  this  kind  the  volume  of  the  products 
is  not  necessarily  larger  than  that  of  the  explosive  mixture ;  indeed,  it 
may  be  less,  as  when  three  volumes  of  hydrogen  and  oxygen  become 
two  of  water.  The  explosive  power  then  must  be  due  to  the  rise  of 
temperature  in  the  gases,  which  is  caused  by  the  heat  of  reaction. 
Gaseous  mixtures  are  not  applied  to  the  ordinary  purposes  of  explo- 
sives, but  they  are  often  the  cause  of  serious  accidents,  and  they  find  a 
limited  use  as  motive  power  in  gas  engines. 

Another  type  of  explosive  mixture  has  likewise  been  the  cause  of  567 
most  serious  accidents — namely,  a  combustible  solid  in  the  form  of 
very  fine  dust  scattered  through  the  air  in  a  more  or  less  confined 
space.  It  will  readily  be  understood  that  minute  particles  of  carbon 
might  be  suspended  in  air  so  close  to  each  other  that  ignition,  started 
at  one  point,  would  flash  quickly  to  neighboring  points  exactly  in 
effect  as  if  it  were  a  gaseous  mixture.  In  such  way  most  disastrous 
explosions  have  occurred  in  flour  mills  and  starch  factories,  where  the 
extremely  fine  dust  of  combustible  starch,  swept  into  the  air  by  some 
accidental  cause,  and  brought  in  contact  with  flame,  has  furnished  the 
necessary  conditions.  The  dust  in  coal  mines  also  has  caused  explosion. 

Explosive  compounds. — Finally,  there  is  still  another  and  most  inter-  568 
esting  type  of  explosive,  in  which  the  closest  kind  of  contact  is  brought 
about.  In  these  the  combustible  and  the  oxidizer  are  proximate  con- 
stituents of  one  individual  substance.  In  theoretical  terms,  they  are 
parts  of  the  same  molecule  instead  of  being  in  neighboring  molecules. 
Therefore  the  explosive  is  a  single  substance  and  not  a  mixture.  How 
this  can  be,  is  understood  in  recalling  the  fact  that  of  potassium  nitrate, 
KaO'N305,  it  is  mainly  the  nitrogen  oxide  which  supplies  oxygen  to  the 
carbon  in  gunpowder.  Now,  if  nitric  acid  could  be  combined  in  a  salt 
with  a  combustible  base — for  example,  one  containing  carbon  and 
hydrogen— the  condition  of  combustible  and  supporter  of  combustion 
would  be  realized  in  one  compound,  and  it  would  only  be  necessary  to 
break  down  the  compound  in  order  that  the  elements  might  recombine 
into  carbon  dioxide,  water,  and  nitrogen.  Such  a  base  is  found  in 
common  glycerine,  which  is  only  one  of  a  numerous  class  of  organic 
bases,  called  alcohols.  The  composition  of  glycerine  is  seen  in  the 
formula,  C3H6(OH)g,  and  its  combination  with  nitric  acid,  after  analogy 
with  the  formation  of  potassium  nitrate,  is  shown  by  the  equations : 

C,H.(OH)»  +  3HNO,  =  C3HB(N03)3  +  3HaO. 
KOH  +  HN03  =  K(N03)+  H80. 


210        ELEMENTARY   PRINCIPLES  OF  CHEMISTRY 

569  This  glycerine  trinitrate  is  more  commonly  known  under  the  less  cor- 
rect name  of  nitroglycerine.     The  following  equation  shows  that  no 
outside  oxygen  is  needed  for  the  complete  combustion : 

2C3H6(N03)3)  =  6COa  +  5H20  +  6N  +  0. 

Nitroglycerine  was  discovered  in  1847,  but  was  practically  unused 
until  about  1863.  Its  successful  application  was  due  to  a  Swede,  Nobel 
by  name,  who  also  discovered  the  method  of  firing  by  detonation.  Nitro- 
glycerine is  made  by  adding  glycerine,  as  a  thin  stream  or  spray,  very 
slowly  to  a  cooled  mixture  of  sulphuric  and  nitric  acids  in  the  most 
concentrated  form  obtainable.  It  is  important  that  all  these  substances 
be  very  pure  and  anhydrous.  The  temperature  of  the  mixture  must  not 
rise  above  30° ;  if  it  does,  there  is  great  danger.  When  the  reaction  is 
over,  the  nitroglycerine  rises  to  the  top  and  is  drawn  off,  or  the  mixture 
is  run  into  water  in  which  the  product  sinks  to  the  bottom  as  an  insolu- 
ble oil.  It  must  then  be  very  thoroughly  washed  until  free  of  acid,  as 
the  presence  of  this  promotes  decomposition  and  dangerous  instability. 
It  is  sometimes  strained  through  felt  filters  for  additional  purification. 

570  Nitroglycerine  is  an  oily,  colorless,  or  nearly  colorless  liquid,  heavier 
than   water,   with   which  it   does   not   mix.     It  is  somewhat  volatile 
at  50°  and  freezes  at  about  8°,  although  the  freezing  point  varies  in 
different  samples.     It  is  poisonous,  and  is  used  as  a  powerful  remedy 
in  medicine.     In  the  open  air,  small  quantities  may  be  burned  without 
explosion,  but  when  heated  to  about  180°,  it  explodes.     It  may  also  be 
exploded  by  a  shock,  either  of  a  blow  or  by  detonation.     It  is  less  sen- 
sitive in  the  frozen  condition  than  in  the  liquid,  and  it  is  not  commonly 
used  in  the  latter  form,  except  in  order  to  "  torpedo  "  gas  and  oil  wells. 

571  The  volume  of  gas  (counting  the  water  as  gaseous)  from  the  explo- 
sion of  one  gram  of  nitroglycerine  is  about  714  cubic  centimeters  reck- 
oned at  0°,  and  the  temperature  is  about  3,000°.    It  is  reckoned  as  from 
four  to  six  times  more  effective  than  powder,  at  least  in  blasting  rock. 
The  velocity  of  detonation   in   the  liquid   is  5,300  feet  per  second. 
Owing  to  its  properties,  nitroglycerine  does  not  need  to  be  confined  in 
order  to  be  effective.     Exploded  on  the  surface  of  a  rock,  it  may  shat- 
ter the  rock,  for  the  action  is  so  quick  that  the  atmosphere  is  practi- 
cally unyielding  during  the  short  interval. 

572  In  order  to  reduce  the  danger  in  handling  liquid  nitroglycerine,  it 
is  absorbed  in  some  solid  which  in  one  class  of  explosives  is  inert,  in  an- 
other class  the  absorbent  is  itself  explosive,  or  at  least  combustible.    Of 
the  first  class,  and  the  most  common  of  all,  is  dynamite,  which  was  in- 
vented by  Nobel.     The  absorbent  is  a  kind  of  clay  made  up  largely  of 
the  silicious  remains  of  minute  organisms.    This  takes  u-p  about  three 


DESCRIPTION   OF  ELEMENTS  AND  COMPOUNDS    211 

times  its  weight  of  nitroglycerine  and  forms  a  plastic  mixture.  The 
velocity  of  detonation  in  dynamite  is  20,000  feet  per  second,  four  times 
that  in  the  liquid,  and  its  effective  intensity  is  greater,  but  in  smaller 
ratio ;  these  facts  are  difficult  of  explanation.  As  absorbents,  mag- 
nesia, powdered  mica,  sawdust,  and  charcoal  are  used  to  some  extent. 

Gun  cotton  is  an  explosive  of  the  same  chemical  type  as  nitro-  573 
glycerine.  It  is  a  nitrate  of  cellulose ;  cellulose  is  the  alcoholic,  organic 
base  which  constitutes  the  fundamental  substance  of  the  plant  struc- 
ture, and  it  is  seen  in  nearly  pure  condition  as  cotton  fiber  and  filter 
paper.  The  nitrate  is  made  from  thoroughly  cleaned  cotton  by  dip- 
ping it  into  the  mixture  of  concentrated  sulphuric  and  nitric  acids.  In 
this  instance,  also,  it  is  very  important  that  the  acids  be  completely 
washed  out,  lest  they  provoke  dangerous  decomposition  ;  therefore  the 
cotton,  which  is  hardly  changed  in  appearance  by  nitrating,  is  reduced 
to  pulp  under  water,  then  washed  and  pressed  into  compact  forms  as 
desired.  When  designed  for  military  purposes,  it  is  allowed  to  retain 
from  16  to  30  per  cent  of  water,  which  renders  it  much  safer,  and  does 
not  interfere  with  its  explosion  by  detonation.  In  this  condition  it  is 
stored,  for  it  is  not  sensitive  to  friction  or  percussion,  nor  to  fire  until 
the  water  is  dried  out  of  it.  Even  when  dry  it  is  not  easily  exploded 
by  percussion,  and  it  burns  quietly  if  unconfined.  When  properly  pre- 
pared, it  is  reckoned  as  "  the  safest  explosive  known."  (Walke.) 

The  composition  of  gun  cotton,  reduced  to  the  simplest  terms,  is    574 
expressed  by  the  formula  C6H702(N08)3.    The  following  equation  shows 
that  it  does  not  contain  enough  oxygen  for  complete  combustion : 

2C8H702(N03)3  +  90  =  12C02  +  7H20  +  6N. 

In  the  gaseous  products  of  its  explosion  (there  are  no  solids,  hence 
no  smoke)  are  found  carbon  monoxide  and  hydrogen,  besides  those  in 
the  preceding  equation.  The  total  volume  of  gas  from  one  gram  of 
gun  cotton  is  given  by  one  observer  as  859  cubic  centimeters,  reckoned 
at  0°.  This  is  more  gas  than  either  gunpowder  or  nitroglycerine  gives, 
and  the  temperature  produced  is  also  higher  than  that  of  gunpowder. 
The  velocity  of  detonation  is  greater  in  wet  gun  cotton  than  in  dry, 
reaching  about  20,000  feet  per  second,  nearly  four  times  the  velocity 
in  nitroglycerine  and  about  the  same  as  that  in  dynamite. 

Gun  cotton  is  used  largely  as  a  high  explosive  for  military  purposes,  575 
in  torpedoes,  and  in  submarine  mines.  It  is  also  used  as  a  constituent 
in  many  other  explosives.  In  some,  additional  oxygen  is  supplied  by 
mixing  with  potassium  or  other  nitrate.  Blasting  gelatin  is  a  mix- 
ture of  mono-  and  di-nitrocellulose  and  nitroglycerine,  which  contains 
some  excess  of  oxygen.  (See  No.  569.)  Nitrocellulose  is  also  the  chief 
15 


212        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

57(5  constituent  of  the  smokeless  powders  which  are  displacing  the  black 
and  the  brown  gunpowder  for  military  and  other  uses.  That  which  is 
prepared  for  the  United  States  navy  contains  nitrocellulose  mixed  with 
barium  nitrate,  potassium  nitrate,  and  calcium  carbonate.  Cordite, 
the  powder  adopted  by  Great  Britain,  contains  nitroglycerine,  nitro- 
cellulose, and  vaseline  (Deering-Thorpe,  F.  H.  Thorp,  Walke). 

17.   CALCIUM 

Ca.—  39.7 

577  History.  —  The  preparation  of  lime,  CaO,  by  the  so-called  burning 
of  limestone,  CaC03,  and  its  use  in  making  mortar,  are  of  great  an- 
tiquity.   In  1756  Black  showed  the  chemical  relation  between  lime  and 
limestone,  and  in  1808  Davy  obtained  the  element  as  a  metallic  powder 
by  the  electrolysis  of  the  chloride.     Matthiessen,  in  1856,  also  by  elec- 
trolysis, succeeded  in  producing  it  as  a  coherent  metal,  and  Moissan  re- 
investigated  it  in  1898. 

578  Natural  occurrence.  —  It  is  never  found  free.     Its  most 
abundant  compound  is  the  carbonate,  which  is  known  in  its 
various  conditions  as  limestone,  chalk,  marble,  coral,  calc- 
spar,  calcite,  etc.     The  sulphate,  CaS04,  is  also  abundant 
under  the  names  of  anhydrite  and  gypsum.     The  phosphate, 
borate,  silicate,  and  fluoride  are  native.     Calcium  salts  are 
present  in  natural  waters,  and  are  essential  to  the  plant 
organism,  accumulating  in  the  leaves,  and  also  essential  to 
the   animal,   occurring   particularly  in   shells,  bones,  and 
teeth.     The  element  is  present  in  the  sun,  and  has  been 
found  in  meteorites. 

579.        Preparation.  —  Moissan    prepared   it   (1898)   by  electro- 
lyzing  fused  calcium  iodide,  CaI2  ,  at  a  dull-red  heat,  also 
by  heating  to  dull  red  a  mixture  of  the  anhydrous  iodide 
and  sodium  in  a  closed  iron  crucible. 
The  reaction  is  : 


CaI2  +  2Na  =  Ca 

The  iodide  and  the  excess  of  sodium  are  dissolved  out  by 
anhydrous  alcohol,  which  has  been  freed  of  dissolved  air, 
and  the  calcium  is  left  as  a  crystalline  powder. 


DESCRIPTION   OF  ELEMENTS  AND  COMPOUNDS    213 

Properties  (Moissan).  —  Calcium  is  a  silver-white,  crystal-  680 
lizable  metal,  soft  enough  to  be  cut  with  a  knife.  Its  spe- 
cific gravity  is  1.85,  and  it  melts  at  760°.  Heated  in  oxy- 
gen to  300°,  it  burns  brilliantly,  with  great  evolution  of 
heat,  forming  the  oxide  CaO.  Also  in  nitrogen  it  burns, 
forming  the  crystallizable  nitride  Ca3N2.  Both  oxide  and 
nitride  are  formed  when  it  burns  in  air.  Heated  in  hydro- 
gen, a  crystalline  hydride,  CaH2  ,  is  formed  ;  and  in  chlorine, 
the  chloride,  CaCl2.  It  combines  also  directly  with  carbon 
(CaC2),  with  silicon,  with  sulphur,  and  with  phosphorus 
(Ca3P2).  A  compound  with  boron,  and  a  second  oxide, 
Ca02,  are  known.  Calcium  decomposes  water  on  contact 
at  ordinary  temperature,  liberating  hydrogen  and  forming 
the  oxide  CaO,  which  combines  with  water  and  acts  as 
base  in  forming  salts.  The  metal  reduces  the  oxides  of 
lithium,  sodium,  and  potassium,  also  carbon  dioxide,  when 
heated  with  them,  but  not  the  oxide  of  magnesium.  The 
hydride,  carbide,  nitride,  and  phosphide  decompose  water 
on  contact  by  reactions,  which  are  thus  expressed  : 

CaII2  +  2H20  =  CaOH20  +  4H. 
CaC2  +  2H20  =  CaOH20  +  C2H2. 

6H0  =  3CaOH0  +  2NH8. 


Lime,  calcium  monoxide,  CaO,  does  not  occur  native.  It  581 
is  made  on  a  large  scale  by  heating  the  carbonate,  CaC03  ; 
the  decomposition  begins  at  about  400°.  This  is  called 
technically,  but  erroneously,  "burning,"  and  the  product 
"  burnt  "  lime,  or  "  quicklime."  Lime  is  a  white  and,  ordi- 
narily, amorphous  solid.  Exposed  to  prolonged  heating  by 
the  oxyhydrogen  flame,  it  slowly  crystallizes  at  the  surface, 
but  by  the  heat  of  the  electric  arc  it  fuses  and  volatilizes, 
forming  colorless,  brilliant  crystals.  If  impurities  —  e.  g., 
alumina  —  are  present,  fusion  takes  place  more  readily,  since 
compounds  with  the  lime  are  formed  which  are  more  fusi- 
ble. The  amorphous  lime  which  is  made  from  the  carbon- 
ate is  hard  and  quite  porous  ;  by  exposure  to  air  it  absorbs 


214        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

water  and  carbon  dioxide  slowly,  and  falls  into  a  soft  pow- 
der, which  is  a  mixture  of  hydroxide  and  carbonate.  This 
makes  quicklime  a  useful  drying  substance,  especially  for 
gases.  On  the  other  hand,  if  lime  is  brought  in  direct  con- 
tact with  a  suitable  quantity  of  water,  combination  takes 
place  quickly  with  liberation  of  much  heat ;  the  hydroxide, 
Ca(OH)2,  is  formed,  and  appears  as  a  soft  dry  powder,  if 
too  much  water  is  not  present.  This  operation  is  called 
"  slaking,"  and  the  product  "  slaked  "  lime.  The  heat  of 
hydration  may  be  sufficient  to  cause  fire  if  combustible 
matter  is  present.  The  crystallized  oxide,  on  contact  with 
air  or  with  water,  changes  very  much  more  slowly  than  the 
amorphous,  and  apparently  it  does  not  dissolve  until  the 
combination  with  water  has  taken  place. 

582  The  hydroxide,  Ca(OH)2,  usually  an  amorphous  powder, 
although  crystallizable,  is  slightly  soluble  in  water,  100  grams 
of  the  latter  dissolving  about  0.18  of  a  gram  of  the  hy- 
droxide at  20°,  but  only  one  half  as  much  at  100°.     The 
solubility,  therefore,  decreases  with   rise  in    temperature, 
which  is  exceptional.     The  solution  has  alkaline  reaction 
and  is  often  called  "limewater."    When  more  hydroxide  is 
present  than  the  water  can  dissolve,  the  mixture  is  called 
"  milk  of  lime."     The  hydroxide  loses  its  water  at  a  red 
heat,  the  decomposition  beginning  even  at  100°  (Kamsay). 

583  Lime  finds  a  great  variety  of  uses,  for  instances :  in 
mortar  and  cements ;  in  making  glass,  bleaching  powder, 
and  soda  (by  the  Leblanc  process) ;  in  purifying  coal  gas 
and  sugar ;  in  preparing  many  chemicals  ;  in  bleaching  and 
dyeing  cotton  fabrics;   in  tanning  leather;    in  obtaining 
metals  from  their  ores ;  and  as  a  disinfectant. 

584  The  monoxide  and  the  hydroxide  act  as  base  and  form 
a  series  of  well  known  salts.     The  chloride,  CaCl2,  when 
anhydrous  is  very  deliquescent,  and  dissolves  abundantly  in 
water  with  evolution  of  heat.     The  crystallized  chloride, 
CaCl2-6H20,  dissolves  with  absorption  of  heat,  and,  mixed 
with  ice  or  snow,  may  reduce  the  temperature  to  —40° ;  this 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    215 

makes  a  convenient  freezing  mixture.  Bleaching  powder, 
and  the  carbonate,  also  the  phosphate,  have  been  sufficiently 
considered  in  other  connections.  The  sulphide,. CaS,  in  the 
impure  form  commonly  made,  is  phosphorescent  and  used 
somewhat  in  making  the  luminous  paints.  The  sulphate, 
CaS04,  known  as  "  plaster  of  Paris,"  is  used  in  cements. 

17a.     Mortar  and  other  Cements 

Preparation  of  lime. — The  primitive  limekiln  or  furnace  was  a  pit  585 
sunken  in  the  ground  of  a  hillside ;  into  it  was  piled  the  limestone 
in  rather  large  lumps,  leaving  an  opening  and  cavity  at  the  bottom 
for  the  fuel.  The  hot  gases  and  the  carbon  dioxide  which  is  liberated 
are  then  free  to  pass  upward  through  the  loosely  packed  material  and 
escape  into  the  atmosphere.  It  is  important  that  the  carbon  dioxide 
be  thus  swept  away  as  produced,  otherwise  the  carbonate  may  be 
reformed.  Permanently  constructed  furnaces  are  now  largely  used. 
Excessive  heating  must  be  avoided,  lest  it  cause  the  beginning  of  fusion , 
which  gives  a  product  that  does  not  easily  slake.  This  is  more  likely 
to  happen  with  impure  limestone.  For  other  reasons  also,  approximate 
purity  is  desirable  in  many  of  the  uses  to  which  lime  is  put. 

Mortar  is  a  mixture  of  lime  and  sand  which  dries  in  the  atmosphere  58(> 
and  hardens ;  it  is  used  as  a  cement,  as  a  covering  for  walls,  and  in 
many  other  ways.  In  its  preparation,  the  quicklime  is  first  slaked  and 
mixed  with  water  to  a  thin  paste.  If  such  a  paste  is  allowed  to  dry,  it 
shrinks  considerably ;  therefore  it  is  mixed  with  sand,  and  in  this  con- 
dition it  is  applied  to  brick  or  stone,  so  that  it  fills  the  separating 
spaces  completely,  and  hardens  to  a  compact  mass  without  shrinkage. 
Sand,  the  grains  of  which  are  sharp  and  not  rounded  by  friction,  is 
preferred,  as  experience  has  shown  that  it  makes  a  better  mortar.  After 
several  days  of  exposure  to  air  the  mortar  "  sets " — that  is,  partly 
hardens.  This  is  due  to  drying.  After  this  change,  a  very  slow  absorp- 
tion of  carbon  dioxide  takes  place,  with  the  formation  of  carbonate, 
and  this  produces  the  second  stage  of  hardening.  The  sand  serves  not 
only  to  increase  the  bulk  of  the  lime,  but  also  its  porosity,  and  thus 
facilitates  the  absorption  of  carbon  dioxide.  If  the  drying  is  too  quick 
or  too  complete,  the  hardening  is  interfered  with,  so  that  moisture 
plays  an  important  part  in  the  change ;  just  how  this  is,  and  how  the 
carbon  dioxide  penetrates  to  the  interior,  are  not  entirely  clear.  It  is 
thought  that  the  sand  is  not  chemically  changed  in  hardening,  although 
in  samples  of  mortar  one  hundred  years  old,  or  older,  the  silica,  from  2 


216       ELEMENTARY  PRINCIPLES  OP  CHEMISTRY 

to  6  per  cent  of  it,  has  been  found  in  combination.  The  mortar  in  the 
Pyramid  of  Cheops,  although  older  than  2000  B.  c.,  is  practically  of  the 
same  composition  as  the  modern  mixture ;  and  other  mortars  of  Phoe- 
nician, Greek,  and  Roman  masonry  have  been  examined  with  similar 
result.  In  some  instances  the  lime  is  found  converted  completely  into 
carbonate,  in  others  only  partly  so. 

Hydraulic  lime. — If  limestone  contains  more  than  about  10  per  cent 
of  clay  (aluminium  silicate)  when  it  is  burned,  it  yields  a  lime  which 
slakes  less  readily  and  with  less  heat,  but  which  sets  or  hardens  when 
in  contact  with  water  or  even  under  water  ;  hence  it  is  called  hydraulic. 
The  hardening  in  this  case  is  due  to  reaction  between  water  and  the 
anhydrous  silicates  and  is  independent  of  carbon  dioxide.  Such  lime 
is  of  value  in  making  hydraulic  mortar  or  cement  which  is  to  be  used  in 
constructions  with  which  water  comes  in  contact.  Certain  natural  anhy- 
drous silicates  of  volcanic  origin,  when  finely  ground  (without  burn- 
ing) and  mixed  with  ordinary  lime,  constitute  another  variety  of  hy- 
draulic cement;  and  blast-furnace  slag,  if  cooled  quickly  from  the 
melted  condition,  is  similarly  used  with  lime.  Still  a  third  variety  is 
made  by  burning  at  a  very  high  temperature  an  artificial  mixture  of 
pulverized  calcium  carbonate  and  clay.  Of  this  variety  is  "  Portland 
cement,"  which  is  made  and  also  imported  in  large  quantity  in  this 
country.  The  materials  are  ground  and  intimately  mixed,  then  burned, 
and  finally  ground  again.  Much  of  the  quality  depends  upon  the 
proper  heating.  The  setting  and  hardening  are  undoubtedly  due  to 
chemical  reaction,  but  its  exact  nature  is  not  easily  explained.  It  is 
supposed  that  silicate  and  aluminate  of  calcium  are  formed  by  the 
heating,  and  that  these  combine  with  water  and  crystallize  more  or 
less,  finally  becoming  as  hard  as  natural  stone. 

Plaster  of  Paris  is  another  variety  of  cement  which  finds  many  uses. 
This  is  made  by  heating  to  120°  or  130°  the  mineral,  gypsum,  which  is 
a  hydrated  calcium  sulphate,  CaS04-2H20.  Only  about  three  fourths 
of  the  water  is  thus  expelled,  so  that  plaster  of  Paris  is  chemically 
(CaS04)2-H20.  When  this  powder  is  mixed  with  water  to  a  creamy 
paste,  heat  is  liberated,  the  mixture  swells  somewhat,  and  quickly  hard- 
ens to  a  white  porous  mass  of  smooth  surface.  If  the  gypsum  is  heated 
to  200°,  all  the  water  is  driven  off  and  the  plaster  does  not  set.  The 
chemical  changes  of  the  hardening  are  explained  as  follows  :  The  com- 
pound (CaS04)2-H20  is  somewhat  soluble,  and  in  solution  slowly  com- 
bines with  water,  thus : 

(CaS04)iH,0  +  3H,0  =  2(CaS04-2H20). 

The  latter  hydrate,  being  less  soluble  than  the  first,  separates  in  minute 
interlacing  crystals.  Plaster  of  Paris  is  used  as  a  wall  finish  in  the  inte- 


DESCRIPTION   OF  ELEMENTS  AND  COMPOUNDS    217 

rior  of  buildings,  also  for  making  casts  and  reproductions  for  which 
the  property  of  expanding  in  setting  makes  it  especially  applicable 
(Hartley-Thorpe  and  F.  H.  Thorp). 

REVIEW  PROBLEMS 

1.  Assume  that  magnesium  is  converted  into  its  iodide  (see  Exp. 
41/b)  by  direct  action,  how  much  iodine  is  theoretically  needed,  and 
how  much  should  the  magnesium  iodide  weigh  f 

2.  Suppose  that  one  gram  of  magnesium  is  to  be  converted  into 
magnesium  pyrophosphate  and  as  such  weighed  ;  suggest  the  practicable 
operations  for  so  doing,  writing  them  out  in  the  form  of  directions  for 
the  experiment,  based  on  your  knowledge  of  the  properties  of  the  sub- 
stances involved  and  your  experience  in  experimentation  (see  Exps. 
446A  and  494). 

3.  Calculate  what  should  be  the  weight  of  the  pyrophosphate  thus 
obtained. 

4.  Suppose  that  dry  magnesium  sulphate  is  to  be  the  starting  point 
for  the  same  result  as  in  2,  in  what  respect  would  you  modify  your 
directions'?    What  quantity  of  the   sulphate  should  yield   the   same 
quantity  of  the  pyrophosphate  that  one  gram  of  magnesium  yields  ? 

5.  Does   aluminium    easily  burn  ?      Suggest  practicable  steps  by 
which  one  gram  of  aluminium  may  be  converted  into  the  oxide  by 
converting  first  into  the  hydroxide.     How  much  should  the  oxide  thus 
obtained  weigh  I 

6.  What   is  the   ratio  between  those   masses   of   magnesium   and 
aluminium  which  exactly  react  with  equal  quantities  of  hydrochloric 
acid  f     Also  with  equal  quantities  of  oxygen  f 

7.  How  much  iodine  should  be  needed  exactly  to  convert  sulphur- 
ous acid  into  sulphuric  acid,  making  enough  of  the  latter  to  neutralize 
exactly  39.8  grams  of  pure  sodium  hydroxide  ? 

8.  Sulphuric  acid  may  be  completely  precipitated  from  solution  by 
adding  sufficient  barium  chloride  solution  ;  barium  chloride  in  crystal- 
lized condition  has  the  formula  BaCl2-2H20 :  calculate  how  much  of 
the  latter  would  be  necessary  to  precipitate  exactly  the  sulphuric  acid 
of  1  gram  of  sodium  sulphate  crystallized  (Na2S04-10H20)? 

9.  How  much  crystallized  silver  nitrate  (AgN03)  is  necessary  to 
precipitate  exactly  the  chlorine  of  1  gram  of  dry  sodium  chloride  f 

10.  What  are  the  relative  masses  of  chlorine  and  of  anhydrous 
nitric  acid  (HN03)  which  are  necessary  to  convert  equal  quantities  of 
ferrous  sulphate,  FeO-S03,  into  ferric  sulphate,  Fea03-3S03  ?    (See  Nos. 
532  and  317,  Part  I.) 

11.  As  between  sodium  nitrate  and  potassium  nitrate  at  the  same 


218        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

price  per  kilogram,  which  is  the  more  economical  material  with  which 
to  effect  oxidation,  other  things  being  equal  ?  What  is  the  ratio  of 
economy  f 

12.  As  between  magnesia  and  lime  at  the  same  price  per  pound, 
which  is  the  more  economical  material  for  liberating  ammonia  from 
ammonium  chloride  1  What  is  the  ratio  of  economy  ? 

G.  GENEKAL  SUBVEY 

589  The  general  survey  made  of  the  first  nine  elements  may 
now  be  extended  to  include  the  seventeen.  A  study  of  the 
fuller  data  of  Table  VII,  No.  590,  brings  out  in  a  striking 
manner  the  peculiar  progression  in  properties  at  first  only 
suggested.  Thus  as  to  melting  point,  beginning  with  so- 
dium, and  again  with  potassium,  one  sees  a  progression 
like  that  which  begins  with  lithium.  The  same  may  be 
said  as  to  the  combining  volume,  as  to  the  heat  of  formation, 
the  valence,  and  the  basic  and  acidic  function  of  the  oxides. 
Especially  with  regard  to  valence  and  the  basic  function  is 
clearly  seen  the  tendency  to  recurring  similarities  at  regu- 
lar intervals  or  periods.  Beginning  with  the  alkali  metal 
lithium,  valence  increases  by  units  to  a  maximum  of  four, 
then  decreases  to  one,  and  starting  again  at  one  with  the 
alkali  metal  sodium,  it  passes  again  through  the  same  values 
to  reach  one  in  the  alkali  metal,  potassium.  In  the  same 
interval,  the  basic  property  diminishes,  disappears,  and  re- 
appears. This  is  the  germ  of  what  is  known  as  periodicity. 
Before  giving  a  more  detailed  study  to  this  important  topic, 
it  is  well  to  consider  some  facts  descriptive  of  five  addi- 
tional elements  which  may  be  presented  collectively. 


DESCRIPTION  OF   ELEMENTS  AND  COMPOUNDS    219 


1. 

Ml 

§£ 
£° 


ombin 
volum 


aa 


590 


It 


Oi    0    r-<    l>    00    JO 

rHt-«>i-l05Tt 
C^CO  |  TH 


1    1    I+  + 


"  CO    «0 

CO  ^JH"    50" 


r-j    GO    OS 


05    GO 


»•  CO    00    0    rH 

SSC<jTHT-(T-i 


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M  M 


10  JO    JH 

T-ic3r^<^ 


JJP-"  — ' 


220        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


21-25.    CHROMIUM,    MANGANESE,    IRON,    NICKEL, 

Cr.— 51.74.  Mn.— 54.57.  Fe.— 55.60.      Ni.— 58.24. 

COBALT 

Co.— 58.6 

591  Following  calcium  in  the  list  of  elements  are  the  three 
substances  scandium,  titanium,  and  vanadium,  of  which 
no  detailed  description  is  judged  necessary  in  this  lim- 
ited course.     Following  these,  still  in  the  natural  order, 
are  five  elements — chromium,  manganese,  iron,  nickel,  and 
cobalt.     These  bear  so  peculiar  a  relation  to  periodicity, 
and  one  in  particular — namely,  iron — so  important  a  rela- 
tion to  every  -  day  life,  that  some  description  of  them  is 
desirable. 

592  History. — Chromium  was  first  identified  in  its  acid-forming  oxide 
in  1797,  but  the  element  was  separated  much  later.    Manganese  dioxide 
was  known  in  very  early  years  and  used  in  making  glass,  but  it  was 
long  confounded  with  the  magnetic  oxide  of  iron  called  loadstone,  and 
the  element  was  not  obtained  until  1774.     Iron  has  been  known  from 
the  earliest  times ;  even  the  use  of  the  metal  is  older  than  recorded 
history.     An  ore  of  nickel  is  mentioned  as  early  as  1694.     The  impure 
metal  was  obtained  in  1754.    Cobalt  in  impure  condition  was  described 
about  1735. 

593  Natural  occurrence. — None  of  these  metals  occurs  native 
to  any  considerable  extent.     Free  iron  and   nickel,  with 
traces  of  cobalt,  are  found  in  meteorites.     Chromium  is 
neither  abundant  nor  widely  distributed.      Manganese  is 
not  abundant  but  is  widely  distributed,  occurring  in  many 
minerals  often  associated  with  iron,  also  to  small  extent  in 
the  soil  and  in  plants  and  animals.     Iron,  on  the  other  hand, 
is  one  of  the  most  abundant  and  most  widely  distributed 
of  the  elements,  as  well  as  one  of  the  most  important  in  its 
relation  to  the  industries.     It  is  found  in  many  minerals, 
also  in  the  soil  and  in  natural  waters.     It  is  an  essential 
constituent  of  plants,  being  found  with  the  green  matter 
named  chlorophyll;  also  of  animals,  constituting  0.2  per 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    221 

cent  of  the  red  coloring  matter  of  the  blood.  Iron  is  also 
present  in  the  sun  and  many  fixed  stars.  Nickel  and  cobalt 
are  generally  found  together,  but  neither  is  very  abundant 
or  common.  Both  exist  in  the  sun. 

The  chief  ore  of  chromium  is  chromite,  or  chrome  iron-  594 
stone,  FeOO203.  Lead  chromate,  PbCr04,  is  found  native, 
and  emerald  with  some  other  green  minerals  owe  their  color 
to  a  small  quantity  of  chromium  which  they  contain.  The 
most  important  ore  of  manganese  is  the  dioxide,  Mn02, 
known  as  pyrolusite,  also  as  the  black  oxide.  Manganese 
is  often  found  with  iron.  Iron  occurs  in  great  abundance 
as  a  sulphide,  FeS2 ,  named  iron  pyrites,  but  this  is  not  used 
as  a  source  of  iron.  For  this  purpose  the  most  important 
ores  are  the  oxides.  Among  these  are  hematite,  Fe203 ,  or 
specular  iron  ore ;  limonite,  the  hydrated  oxide,  or  brown 
hematite  ;  and  magnetite,  or  loadstone,  Fe304 .  Spathic  ore 
or  siderite  is  the  native  carbonate,  FeC03.  Nickel  occurs 
in  combination  with  sulphur,  also  with  arsenic,  and  as 
oxide  and  silicate.  Cobalt  in  its  most  common  ore  is  com- 
bined with  sulphur  and  arsenic. 

Preparation. — These  elements  are  obtained  in  the  metallic  595 
condition,  but  not  pure,  through  the  removal  of  oxygen 
from  their  oxides  by  heating  with  carbon.  Iron  and  nickel 
are  thus  commercially  obtained,  also  alloys  of  iron  with 
manganese  and  chromium.  The  elements  are  obtained  in 
purer  condition  from  the  chlorides  by  electrolysis  or  by 
heating  with  magnesium,  or  in  the  cases  of  iron,  nickel, 
and  cobalt,  by  reducing  their  pure  oxides  with  hydrogen. 
In  nickel  plating,  the  metal  is  deposited  electrolytically. 
The  commercial  preparation  of  iron  will  be  considered  in  a 
following  section. 

Properties.— These  elements  are  all  metallic,  and  in  the  596 
compact  condition  they  are  grayish-white,  hard,  and  may 
be  highly  polished.     Their  melting  points  are  high  but  not 
accurately  enough  determined   to   permit   of  satisfactory 
comparison.     That  of  chromium  is  probably  the  highest  of 


222        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


the  five,  and  manganese  volatilizes   at  high  temperature. 
Some  other  data  are  given  below  : 


597 


NAME. 

Sp.  Gr. 
(H20  =  l) 

Comb, 
vol. 

Formation  heat 
of  chlorides. 

Solubility  of  chlorides  in 
100  of  water. 

Chromium 
Manganese 
Iron  

6.9 

7.4 
8.1 

7.5 

7.4 
6.9 

f 

MnCla=  112,000 

FeCla  =  82,100 

Very  soluble. 
62  at  10° 
50  at  19° 

Nickel.... 
Cobalt  .... 

about  9.0 
about  9.0 

6.5 
6.5 

NiCl2  =  74,500 
CoCla  =  76,500 

Slightly  soluble  at  100° 
43  at  0° 

Iron,  nickel,  and  cobalt  are  attracted  by  the  magnet,  the 
others  not. 

598  They  burn  in  oxygen,  and,  except  chromium,  oxidize 
in  moist  air  and  decompose  water   at   high  temperature, 
but  manganese  oxidizes  readily  in  the  air  and  decomposes 
water  at  ordinary  temperature.      They  combine   directly 
with  the  halogens,  with  boron,  carbon,  silicon,  sulphur,  and 
phosphorus.      They  dissolve  in  dilute  hydrochloric   acid, 
chromium,   and    nickel   with   the    least    readiness.     None 
shows  a  lower  valence  than  two,  and  all  form  an  oxide 
of  the   type   MO,  and   a   hydroxide,  M(OH)2,  which  act 
as   bases;   chromium  monoxide,  CrO,  has  not  been  sepa- 
rated.    These   hydroxides  tend   to  take  up  more  oxygen 
but  with  decreasing  readiness,  which  becomes  almost  zero 
in  nickel.     The  following  table  shows  the  oxides  of  the 
group : 

599  (1)  Chromium  CrO(?),Cr208,Cr09,Cr08,  CrOCr208. 

(2)  Manganese  MnO,Mna03,Mn02,MnOs,Mna07,MnOMn203. 

(3)  Iron  FeO,Fe203,  Fe03(?)  FeOFe208.  „ 

(4)  Nickel          NiO,Ni203,  NiONi208. 

(5)  Cobalt          CoO,Co208,  CoOCo208. 

600  All  the  monoxides  act  as  bases,  and  the  corresponding 
salts  of  chromium  and  iron  tend  to  pass  into  salts  of  the 
next  higher  oxide.     This  property  shows  itself  in  less  degree 
with  cobalt. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    223 

The  oxides  of  the  type  M203,  the  so-called  sesquioxides,  601 
act  as  bases  in  forming  salts,  except  that  of  nickel,  in  which 
the  basic  function  is  zero.  It  is  only  feeble  in  manganese 
and  cobalt.  At  the  same  time  the  acidic  function  begins 
to  appear  in  the  chromium  oxide,  Cr203 ,  for  it  dissolves  in 
sodium  and  potassium  hydroxides,  but  is  reprecipitated  on 
boiling.  Possibly  further  evidence  of  acid  function  in  the 
sesquioxides  may  be  seen  in  the  compounds  MgO-Fe203  and 
ZnOMn203.  It  is  doubtful  if  the  dioxide,  Cr02,  acts  either  602 
as  base  or  acid,  while  Mn02  seems  to  act  very  feebly  in  both 
capacities.  The  basic  function  entirely  disappears  in  the 
trioxides,  Cr03,  Mn03,  and  Fe03,  which  as  acids  form  the  603 
chromates,  manganates,  and  ferrates.  The  trioxides  lose  a 
part  of  their  oxygen  with  a  readiness  which  increases  from 
chromium  to  iron ;  so  that  the  latter,  Fe03 ,  has  not  been 
obtained  free. 

Of  the  still  higher  oxides,  that  of  chromium,  Cr207,  has  604 
not  been  obtained,  and  its  existence  even  is  doubtful.  That 
of  manganese,  Mn207 ,  acts  only  as  acid,  forming  the  per- 
manganates, of  which  potassium  permanganate  is  an  exam- 
ple, K2OMn207.  This  also  loses  a  part  of  its  oxygen, 
as  has  been  seen  in  the  illustrative  experiments  involving 
its  use. 

The  oxides  of  the  type  M304  are  sometimes  regarded  as  605 
made  up  of  MO  and  M203  in  combination.    They  are  formed, 
that  of  iron  for  example,  by  heating  the  metal  in  air  or  oxy- 
gen.    The  scales  which  form  on  heating  a  bar  of  iron  are 
this  oxide.     These  oxides  do  not  form  distinctive  salts. 

All  these  metals  show  remarkable  variation  in  properties  606 
caused  by  the  presence,  even  in  small  proportion,  of  im- 
purities such  as  carbon,  silicon,  and  phosphorus.  As  it  is 
difficult  to  avoid  their  presence  in  the  prepared  metals,  de- 
scriptions differ  in  many  points.  The  influence  of  these 
substances  on  the  properties  of  the  metal  has  important 
bearing  on  the  industrial  use  of  the  latter,  which  in  the 
case  of  iron  is  very  extensive. 


224        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


23a.   Commercial  Iron 

607  The  commercial  forms  of  this  most  important   metal  are  usually 
grouped  under  three  heads — cast  iron,  steel,  and  wrought  iron.     These 
differ  very  considerably,  especially  as  to  their  physical  properties,  al- 
though chemically  the  difference  is  chiefly  as  to  the  proportion  of  car- 
bon which  they  contain,     As  this,  in  part  at  least,  is  combined  with  the 
iron,  evidently  the  difference  in  properties  should  not  be  regarded  as 
due  entirely  to  impurities,  but  to  some  extent  as  the  difference  of  true 
compounds.     At  the  same  time  there  seems  to  be  no  sharply  dividing 
line  between  the  several  varieties,  and  they  pass  gradually  into  each 
other.     Wrought  iron  is  the  purest  variety,  containing  generally  less 
than  0.15  per  cent  of  carbon.     Cast  iron  contains  from  1.5  to  6  per 
cent  of  carbon  and  is  the  most  impure,  while  steel  is  between  the  two. 
In  cast  iron  the  carbon  is  partly  combined  with  the  iron  as  a  carbide, 
and  this,  when  the  metal  is  dissolved  in  acid,  forms  a  hydrocarbon 
with  the  hydrogen  of  the  latter.     The  uncombined  carbon  appears  then 
as  graphite.     The  total  carbon  appears  in  the  latter  condition,  when 
the  metal  is  dissolved  by  a  copper  salt.    (Compare  Exp.  17/4  and  note.) 
Two  subvarieties  of  cast  iron  are  recognized,  the  white  and  the  gray. 
In  the  former  the  combined  carbon  predominates,  in  the  latter  the 
graphite.     The  gray  variety  is  softer  and  melts  at  a  higher  tempera- 
ture,  but    is    better  for  casting  than  the  white  because  more  fluid. 
Slow  cooling  favors  the  production  of  the  gray,  rapid  cooling  of  the 
white,  perhaps  because  the  carbides,  formed  at  the  high  temperature, 
tend  to  decompose  on  cooling. 

608  Silicon  is  also  an  impurity  of  cast  iron,  averaging  from  1  to  4  per 
cent.     In  these  proportions  it  tends  to  make  the  metal  soft  and  strong 
and  suitable  for  casting,  but  in  larger  proportion  it  renders  it  hard  and 
brittle.     High  temperature  and   silicious  "slags"  in  the   process  of 
manufacture  tend  to  increase  the  quantity  of  silicon  in  the  product. 

609  Sulphur  is  an  objectionable  impurity,  which  is  present  only  in  small 
quantity — a  few  hundredths  of  1  per  cent  in  good  cast  iron.     High  tem- 
perature in  making,  and  the  presence  of  silicon  or  manganese  in  the 
metal  and  of  lime  in  the  slag,  tend  to  eliminate  the  sulphur. 

Manganese  is  always  present  in  cast  iron.  With  20  per  cent  or  more 
the  product  is  known  as  ferro-manganese.  Its  presence  is  generally 
advantageous. 

610  Phosphorus  has  a  bad   effect  in  making  steel  and  wrought  iron 
brittle. 

The  following  table  gives,  for  illustration,  the  composition  of  sam- 
ples of  cast  iron,  steel,  and  wrought  iron  : 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    225 


CONSTITUENTS. 

Gray 
cast 
iron. 

White 
cast 
iron. 

Besse- 
mer soft 
steel. 

Siemens 
soft  steel 

Hard 
steel. 

Cruci- 
ble 
steel. 

Wrought 
iron. 

Graphitic  carbon 
Combined      " 
Silicon  

2.65 

0.08 
2.95 

0.20 
2.00 
0.71 

0.126 
0.135 

0.167 
0.023 

1.144 
0.166 

0.36 
0.02 

0.06 
0.04 

Manganese 

0  40 

0  50 

0.158 

0.044 

0.104 

0.30 

0.08 

Phosphorus 

1.84 

0.47 

0.06 

0.062 

0.03 

0.20 

Sulphur  

0.06 

0.19 

0.014 

0.013 

0.02 

0.05 

Iron 

92  02 

95  93 

The  melting  point  of  wrought  iron  is  given  as  varying  from  1,900°  to 
2,100°,  of  steel  from  1,300°  to  1,400°,  and  of  cast  iron  from  1.100°  to  1,200°. 

The  manufacture. — The  ores  commonly  used  in  making  iron  are  the 
oxides  or  carbonates.  In  some  instances  these  undergo  a  preliminary 
heating  or  calcination,  for  the  purpose  mainly  of  converting  the  ferrous 
compounds  into  the  ferric,  and  of  making  the  material  more  porous. 

The  ore  is  reduced  in  the  Hast  furnace.  This  is  an  upright  shaft,  like 
a  large  chimney,  but  considerably  narrower  at  the  top  and  bottom  than 
at  the  middle,  so  that  the  upper  and  lower  thirds  of  its  height  are  conical 
instead  of  cylindrical.  This  is  lined  with  fire-brick,  the  outside  being 
built  of  iron  plates.  The  charge  is  introduced  at  the  top  and  consists  of 
the  ore  with  alternate  layers  of  coke  and  limestone.  The  blast  of  air, 
under  a  pressure  varying  from  four  to  ten  pounds  per  square  inch  and 
at  a  temperature  of  200°  to  400°,  is  forced  in  at  the  base.  The  follow- 
ing figures  give  an  approximation  of  the  relative  quantities  employed: 


Charge. 
Calcined  ore  .  .  . 

Cwt. 

48 

Products. 
Iron 

Cwt. 
.     20 

Limestone  . 

12 

Slag 

30 

Coke 

20 

Waste  gases 

130 

Blast  

100 

180 

180 

The  chemical  reactions  are  complicated.  Their  general  character 
may  be  thus  described :  The  fuel  is  converted  into  carbon  dioxide  and 
monoxide.  The  ore  in  the  first  part  of  its  descent  is  rapidly  heated  to 
low  redness.  At  this  temperature  the  monoxide,  which  constitutes  36  per 
cent  of  the  gases  at  this  portion  of  the  furnace,  acts  on  ferric  oxide  thus : 

Fe308  -f-  3CO  =  2Fe  -f  3C02. 

The  iron  is  in  the  form  of  metallic  sponge,  the  temperature  not  being 
high  enough  to  melt  it.    Below  the  region  of  this  reaction  the  lime- 


611 


612 


226        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

stone  is  decomposed,  and  the  dioxide  which  is  produced  aids  in  pro- 
tecting the  iron  from  reoxidation.  As  the  material  settles  in  the 
furnace  the  temperature  increases,  and  carbon  is  formed  by  the  reduc- 
-  tion  of  the  monoxide  and  is  deposited  in  the  porous,  spongy  iron  in  a 
manner  favorable  to  combination  with  the  latter.  This  takes  place 
when  the  suitable  temperature  is  reache'J,  and  as  a  consequence  the 
product  becomes  fusible  in  the  existing  conditions  ;'  the  molten  metal 
accumulates  in  the  lowest  part  of  the  furnace,  called  the  "  hearth  "  or 
"  crucible."  The  silica  combines  with  the  lime,  and  alumina  if  pres- 
ent, of  the  charge  and  makes  the  fusible  slag  which  floats  on  the 
heavier  molten  metal.  The  latter  is  drawn  off  at  suitable  intervals  and 
run  into  rough  molds.  In  this  form  it  is  known  as  "  pig  iron." 

613  From  this  cast  iron  both  wrought  iron  and  steel,  the  former  first,  are 
made  by  processes  of  refining.     These  consist  chiefly  in  burning  out 
the  carbon.     In  an  older  method,  now  little  used,  this  is  accomplished 
by  melting  the  cast  iron  on  a  hearth  and  directing  upon  it  a  blast  of 
air.     The  carbon  burns  away  to  the  monoxide,  the  silica  combines  with 
ferrous  oxide,  also  formed,  and  produces  a  slag  which  protects  the 
iron  from  further  oxidation.     This,  in  consequence  of  losing  carbon, 
has  a  higher  melting  point  and  becomes  pasty.     The  semi-fused  mass, 
called  the  "  bloom,"  is  removed  from  the  furnace  and  freed  of  the  slag 
by  beating  under  the  steam  hammer. 

614  A  modification  of  this  process,  known  as  puddling,  was  introduced 
in  1784,  and  further  modified  about  1820.     The  cast  iron  is  heated  by 
the  furnace  flame  on  a  hearth  made  of  iron  "  scales  "  (oxide).     The  car- 
bon is  burned  by  the  oxygen  of  the  iron  oxide*  and,  as  the  metal  melts 
and  finally  becomes  pasty,  it  is  stirred   mechanically  or  "puddled." 
The  "  blooms  "  are  hammered,  as  before. 

615  A   third   method  is  that   of   Bessemer,  which  has  revolutionized 
the  steel  industry.     It  was  patented  in  1856.     In  this  the  iron,  which 
should  contain  not   more  than   a  few  hundredths  per  cent  of  phos- 
phorus nor  more  than  2  or  3  per  cent  of  silicon,  is  turned  in  molten 
condition  from  the  blast  furnace  into  an  egg-shaped  vessel,  called  the 
"  converter,"  which  has  been  previously  heated.     This  is  so  supported 
thatrUT  can   be  inverted,  like   a   huge    pitcher.     It  is   fitted  with  a 
movable   false    bottom,   and    is   lined   with    some   silicious   material. 
While   the   converter   is  in   horizontal    position    it    is  charged   with 
molten  cast  iron,  weighing  from  five  to  ten  tons.     A  blast  of  air  un- 
der the   pressure  of  about   20   pounds  to   the    square   inch  is  then 
blown  through  the  false  bottom,  and,  the  vessel  having  been  restored 
to  the  vertical  position,  the  air  is  forced  through  the  melted  metal. 
By  this  means  the  silicon  is  burned  to  the  dioxide  and  passes  into 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    227 

the  slag.  The  carbon  is  next  burned,  and  the  flame  of  the  monox- 
ide appears  above  the  metal  until  the  carbon  is  all  eliminated.  The 
temperature  is  sufficient  to  keep  the  metal  in  liquid  condition,  and  it 
may  be  thus  drawn  off  into  molds.  In  this  degree  of  purity,  however, 
it  is  too  soft  for  many  purposes,  so  carbon  is  added  by  putting  into  the 
converter  after  the  refining  is  finished,  but  before  the  metal  is  poured, 
the  necessary  quantity  of  iron  containing  a  known  amount  of  carbon, 
and  often  also  some  manganese.  By  this  means  steel  is  produced  which 
contains  the  desired  proportion  of  carbon.  By  this  Bessemer  process 
the  sulphur  and  phosphorus  are  not  removed,  but  remain  combined 
with  the  iron ;  hence  the  need  that  the  original  cast  iron  shall  not  con- 
tain these  impurities  in  objectionable  proportion. 

In  the  basic  Bessemer  process  the  lining  of  the  converter  is  made  616 
of  lime  and  magnesia  instead  of  the  acidic  silicious  material,  and  lime 
is  added  to  the  charge.  By  this  modification  iron  containing  phos- 
phorus may  be  used,  since  the  latter  is  converted  in  the  presence  of 
these  bases  into  phosphates,  and  the  sulphur  into  sulphates,  which  pass 
into  the  slag;  but  it  is  important  that  the  iron  be  low  in  silicon. 
This  phosphoric  slag  is  used  as  a  source  of  phosphates.  (See  No.  502, 
Part  I.) 

In  the  Siemens- Mar  tin  process,  by  improved  methods  of  heating,  617 
cast  iron  is  melted  on  a  hearth  and  decarbonized  by  adding  the  suitable 
quantity  of  wrought  iron  or  steel  scrap,  and  the  product  is  still  kept  in 
fused  condition.  This  is  also  known  as  the  "  open-hearth  "  process, 
and  is  operated  in  both  the  acidic  and  basic  modifications.  It  has  the 
advantage  over  the  Bessemer  of  more  easy  control. 

Another  variety  of   steel   is   made   by   the   cementation    process.    618 
Wrought-iron  bars  are  placed  in  fire-clay  boxes,  packed  with  charcoal, 
and  kept  at  red  heat  for  several  days.     In  some  manner  not  well  un- 
derstood the  carbon  is  absorbed  and  steel  produced,  which  is  forged 
under  the  hammer. 

Steel,  when  quickly  cooled  after  heating  to  a  high  temperature,  is    619 
made  harder ;  if  the  temperature  is  very  high,  the  steel  is  also  brittle, 
but  if  somewhat  lower  it  is  left  elastic.     If  the  cooling  is  slow,  it  is 
softer  and  tougher.     These  changes  are  technically  called  hardening, 
tempering,  and  annealing  (Turner-Thorpe  and  Ramsay). 


H.  THE  LAW  OF  PEKIODICITY 

The   details   of   description    through    which  we  have  620 

passed  have,  no  doubt,  seemed  to  you  tedious  at  times,  but 
16 


228        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

if  by  this  presentation  you  have  been  brought  not  only  into 
acquaintance  with  a  considerable  number  of  substances,  all 
of  scientific  and  many  of  practical  importance,  but  in  addi- 
tion shall  have  been  brought  to  a  fair  appreciation  of  the 
significance  of  the  great  law  of  periodicity,  no  student  of 
you  should  grudge  the  time  and  labor ;  for,  if  the  writer 
be  not  wrong,  this  may  justly  be  reckoned  one  of  the  most 
beautiful  and  significant  generalizations  to  be  found  in  the 
scientific  study  of  nature.  It  seems  so  simple  and  so  evi- 
dent in  the  facts  set  forth,  that  one  wonders  it  should  not 
have  been  earlier  discovered  ;  there  will  be  interest,  there- 
fore, in  considering  very  briefly  some  of  the  ideas  which 
preceded  the  discovery. 

Classification. — Early  in  the  development  of  chemistry 
attempts  were  made  to  classify  the  elementary  substances 
according  to  similarities  into  groups  or  families,  the  mem- 
bers of  which  should  possess  certain  properties  in  common ; 
just  as  in  other  branches  of  natural  science,  plants  and  ani- 
mals are  classified  by  their  resemblances.  As  illustration 
are  cited  some  of  the  families  suggested  by  Dumas,  an  emi- 
nent French  scientist  (1828).  Separating  the  elements 
first  into  metals  and  non-metals,  he  divided  the  latter  into 
five  families  : 

1st.  3d.  3d.  4th.  5th. 

Hydrogen.     Fluorine.  Selenium.  Xitrogen.  Boron. 

Chlorine.  Sulphur.  Phosphorus.  Silicon. 

Bromine.  Oxygen.  Arsenic.  Carbon. 
Iodine. 

Similar  groups  among  the  metals  were  made,  for  example  : 

Lithium.  Calcium. 

Potassium.  Strontium. 

Sodium.  Barium. 

Lead. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    229 

Now,  all  classification  of  this  kind  implies  the  selection  622 
of  some  few  properties,  the  common  possession  of  which 
shall  constitute  the  basis  for  the  grouping.  This  selection 
is  arbitrary,  and  the  determination  of  how  many  and  what 
properties  shall  be  chosen  is  generally  influenced  by  no- 
tions of  the  relative  importance  of  this  or  that  property  or 
resemblance.  Thus  it  comes  about  that  when  attempt  is 
made  to  put  objects  of  nature  in  groups  thus  constituted, 
difficulty  is  very  frequently  met,  for  individuals  are  found 
which  do  not  fit  into  the  groups — individuals  which  may 
perhaps  be  placed  equally  well  in  one  as  in  another  group, 
or  perhaps  may  not  be  satisfactorily  placed  in  any.  Never- 
theless, classification  of  this  kind,  although  imperfect,  is  of 
practical  use,  but  an  important  advance  upon  this  is  gained 
in  recognizing  that  differences  as  well  as  resemblances  must 
be  taken  into  account. 

Numerical  relations. — Early  attempts  were  made  also  to  623 
trace  simple  numerical  relations  between  similar  elements. 
In  this  connection  Dumas  (1857)  may  be  again  mentioned, 
and  also  Professor   Cooke,  of  Harvard  University  (1854). 
For  example,  the  following  relations  were  pointed  out : 


a  =  16 

d=   8 


=  24( 
=   81 


o 
16 
a 

S 
32 
a  +  2d 

Se 
80  (79) 
a  +  8d 

Te 
128  (127) 
a  +  14d 

Li 

7 
a 

Na 
23 
-a  +  2d 

K 
39 
a  +  4d 

Mg 
24 
a 

Ca 

40 

a  +  2d 

Sr 

88(87.5) 
a  +  8d 

Ba 

136  (137) 
a  +  14d 

Front's  hypothesis.— As  early  as  1815  Prout  suggested  624 
that  the  numbers  at  that  time  assigned  as  combining 
weights  were  whole  numbers  or  approximated  whole  num- 
bers, and  therefore  that  the  elements  might  be  themselves 
built  up  from  some  one  elemental  substance,  probably  hy- 
drogen. This  led  to  much  speculation,  and  finally  to  rede- 


230        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

terminations  of  the  combining  weights.  To  the  work  of 
Stas  (1860-'65)  in  this  matter  reference  has  elsewhere  been 
made  (see  No.  145).  His  results  reached  the  highest  de- 
gree of  accuracy  up  to  that  time  attained,  and  still  remain 
unsurpassed.  The  outcome  proved  that  the  combining 
weights  in  many  instances  could  not  be  reckoned  as  whole 
numbers.  Dumas  then  argued  that  they  were  exact  multi- 
ples of  one  half.  But  clearly,  if  speculation  is  to  go  to  this 
extent,  the  exact  combining  weights  need  be  no  obstacle, 
for  by  choosing  a  basal  quantity  sufficiently  small  any  set 
of  numbers  may  be  reckoned  as  exact  multiples  of  the  for- 
mer. This  conception  that  the  elements  may  have  been 
derived  from  some  single  primitive  substance  is  known  as 
the  unitary  theory  of  matter,  and  it  still  receives  more  or 
less  attention. 

625  Periodicity. — The  arrangement  of  the  elements  in  the 
order  of  increasing  combining  weights  was  first  proposed 
in  1853  by  Gladstone,  an  English  chemist,  but  there  was 
much  inaccuracy  in  the  values  of  that  day,  and  he  failed 
to  discover  what  was  later  revealed  by  a  similar  arrange- 
ment.    The  first  clear  recognition  and  formulation  of  the 
law  of  periodicity  is  generally  credited  to  Mendel^eff,  a 
Russian,  and  to  Lothar  Meyer,  a  German,  who  published 
their  views  at  nearly  the  same  time  (1869)  and  independ- 
ently of  each  other.     The  name  of  the  former  is  more 
commonly  associated  with  the  law.     After  the  law  as  an- 

.  nounced  by  them  had  received  very  general  attention,  it  was 
discovered  that  in  1864  an  Englishman  named  Newlands 
had  published  a  paper  in  which,  under  the  name  of  "  The 
Law  of  Octaves,"  he  seemed  to  have  recognized  in  a  meas- 
ure the  phenomenon  which  was  later  and  better  named 
periodicity.  Newlands's  work,  however,  received  but  little 
attention  at  the  time. 

626  The  law  may  be  thus  formulated :  The  elements  being 
arranged  in  the  order  of  increasing  combining  weights,  their 
properties  vary  from  element  to  element,  but  tend  to  return 


DIMITRI  IVANOVITCH  MENDELEEFF 

B.  Siberia,  1834. 
(See  Nos.  625,  638,  639,  641.) 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    231 

to  similarity  at  regular  intervals  or  periods.  This  is  ex- 
pressed more  technically  as  follows  :  The  properties  of  the 
elements  are  periodic  functions  of  their  combining  weights. 
The  groupings  brought  about  under  the  law  are  conven- 
iently set  forth  in  tabular  form,  as  seen  in  Table  VIII,  on 
the  following  page. 

The  Elements  by  Periods 

Thus  tabulated,  the  similar  elements  fall  into  the  ver- 
tical columns,  usually  designated  as  groups  or  families,  and 
the  horizontal  rows  constitute  the  periods.  (Hydrogen  is 
not  included  in  the  table.  It  may  be  looked  upon  as  the 
sole  representative  of  one  period.)  The  periodic  variation 
of  properties  becomes  clearly  evident  in  the  first  and  second 
periods.  It  is  to  be  particularly  noted  that  the  change 
from  extreme  acidic  to  extreme  basic  function  is  abrupt  in 
passing  from  fluorine  to  sodium,  and  that  the  valence  is 
unchanged.  The  same  is  true  in  passing  from  chlorine  to 
potassium.  In  the  third  period  the  placing  of  manganese 
in  the  sixth  group  is  one  of  the  unsatisfactory  and  puzzling 
features  of  the  scheme,  for  it  is  rather  difficult  to  find  any 
close  relationship  between  it  and  chlorine  and  fluorine.  It 
is  distinctly  metallic  and  the  lower  oxide,  MnO,  acts  as 
base,  while  the  oxides,  Mn206  and  Mn207,  act  as  acids.  It 
seems  never  to  act  as  a  monad.  Between  manganese  and 
copper,  which  is  placed  in  Group  I,  are  three  metals — iron, 
nickel,  and  cobalt — whose  combining  weights  are  close  to- 
gether, and  whose  properties  are  very  similar.  They  act 
almost  exclusively  as  bases,  and  they  show  no  valence  less 
than  two.  Then  follows  copper,  which  acts  only  as  a  base 
and  has  a  valence,  in  some  compounds,  of  one,  like  the 
alkalies,  and  in  others  a  valence  of  two,  like  the  iron, 
nickel,  and  cobalt.  These  three  elements,  therefore,  make 
the  change  gradual  from  Group  VII  to  Group  I,  and  they 
constitute  what  is  called  a  transition  group. 


232        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


627 


* 


3.9 

N 
or 


_;OG  ! 


*I 


+ 
00  I 


HI 


co   i 

S7 


* 


J 

oo  i 


NN  1  N 


"I 


51, 

S|  + 


ei         od 


DESCRIPTION  OP  ELEMENTS  AND  COMPOUNDS    233 

From  bromine,  Group  VII,  period  4,  which  is  very  simi-  629 
lar  to  chlorine,  the  change  is  again  abrupt  to  rubidium, 
period  5,  which  greatly  resembles  potassium.  On  the  other 
hand,  the  passage  from  period  5  to  period  6  is  through  the 
transition  group  of  three  elements,  but  the  representative 
of  the  seventh  group  in  this  period  is  lacking.  From 
period  6  to  period  7  the  change  from  iodine  to  caesium  is 
abrupt.  The  last  portion  of  period  7,  the  whole  of  period 
8,  and  the  first  portion  of  period  9  are  lacking,  although 
possibly  some  of  the  rare  elements  (Nos.  53-60,  Table  XI, 
Xo.  644)  which  are  not  yet  sufficiently  well  known  may 
later  fill  some  of  the  vacant  places. 


The  Elements  by  Groups 

The  consideration  of  the  groups  brings  out  some  addi-  630 
tional  features.  Thus  in  Group  I,  after  the  second  period, 
the  resemblance  between  potassium,  K,  rubidium,  Eb,  and 
caesium,  Cs,  is  much  more  marked  than  between  these 
and  copper,  Cu,  silver,  Ag,  and  gold,  Au.  The  former 
three  are  also  more  like  sodium  and  lithium  than  are  the 
latter  three.  The  former  are  set  off  to  the  left  and  the  lat- 
ter to  the  right  of  the  column.  It  is  notable  that  they  alter- 
nate. The  same  plan  is  followed  in  all  the  other  groups, 
but  the  divergence  in  properties  between  the  left-hand  and 
right-hand  series  is  especially  marked  in  Groups  I,  II,  VI, 
and  VII. 

Several  instances  may  be  noted  of  approximately  equal 
differences  between  successive  combining  weights  in  the 
vertical  columns.  (See  also  No.  623.) 

The  comparison  of  properties  in  vertical  columns,  as  631 
before  was  done  in  the  horizontal  rows,  shows  the  progres- 
sion of  properties  also  in  this  direction.  Some  such  nu- 
merical values  for  Groups  I  and  II  are  tabulated  on  the 
following  page,  in  order  to  make  the  relation  quickly  evi- 
dent to  the  eye  : 


234       ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

TABLE  IX 

632  Melting  Points 

I  II 

Li  180°  Gl   1,230° 

Na  96°  Mg  500°-600° 

K    62°          Cu  1,330°  (?)  Ca  760°         Zn    420° 

Kb  39°  Ag  1,040°  Sr     ?  Cd    320° 

Cs  27°  Au  1,240°  Ba   ?  Hg  -39° 

633  Combining  Volumes 

I  II 

11.8  4.9 

23.2  13.8 

45.1  7.1  21.2  9 
56.5              10.1                    34.8              13 

70.2  10.1  37  14.6 

634  Formation  Heat  of  Oxides 
I  II 

141,200  ? 

100,400  143,400  (?) 

98,200  40,800  145,000  85,800 

?  5,900  128,400  66,400  (?) 

?  124,200  20,700 

635  Formation  Heat  of  Chlorides 

I  II 

93,800  ? 

97,600  151,000 

104,300      32,850  169,800     97,200 

29,400  184,600     93,200 

?         5,800  194,700     53,200 

636  Solubility  of  Chlorides 

I  II 

63.7  (0°)  Very  sol. 

35.7  (1°)  52.2  (0°) 

28.7  (1°)   Insol.  50  (0°)    300   (19°) 

76.4  (1°)   Insol.  44.5  (1°)    143   (20°) 

?      Insol.  31.2  (1°)     7.39  (20°) 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS    235 

The  law  of  means. — It  is  evident  from  data  of  the  kind  637 
cited  that  each  element  tends  to  be  intermediate  in  its 
properties  between  the  element  which  precedes  it  and  that 
which  follows  it,  both  in  the  periods  and  in  the  groups. 

Mendeleeffs  predictions. — At  the  time  that  Mendel^eff  638 
published  his  table,  based  on  the  law  of  periodicity,  there 
was  no  element  in  the  list  between  calcium,  II  3,  and  tita- 
nium, IV  3.  He  saw  clearly  that  the  latter  should  be  placed 
in  Group  IV,  from  its  resemblance  to  silicon  and  carbon. 
He  therefore  left  the  space  III  3  unoccupied.  Also  be- 
tween zinc,  II  4,  and  arsenic,  which  evidently  belonged  in 
V  4,  no  element  was  known.  He  therefore  left  two  blank 
spaces  at  these  points.  But,  more  than  this,  confident  in 
the  fundamental  truth  of  the  law  which  he  had  announced, 
he  affirmed  the  probable  existence  of  elements  with  prop- 
erties which  would  fit  them  in  these  vacant  spaces,  and 
he  predicted  their  ultimate  discovery.  Furthermore,  he 
predicted  with  considerable  definiteness  their  properties 
in  several  respects,  including  combining  weight,  valence, 
melting  point,  solubility,  basic  and  acidic  function,  etc. 
In  1875  a  new  element  was  discovered  by  Lecoq  de  Bois- 
baudran,  a  Frenchman,  and  named  by  him  gallium,  in  honor 
of  his  country.  Its  properties  were  found  to  agree  almost 
item  for  item  with  those  predicted  by  Mendeleeff  for  the 
unknown  element,  III  4.  In  1879  another  new  element 
was  discovered  by  Mlson  and  named  scandium,  in  honor  of 
Scandinavia.  This  was  found  to  be  Mendeleeif  s  unknown 
element  III  3,  agreeing  closely  with  the  predicted  proper- 
ties. In  1886  a  third  remarkable  verification  of  the  law 
was  made  in  the  discovery,  by  Winkler,  of  an  element  which 
he  named  germanium,  and  which  corresponds  closely  with 
the  element  predicted  for  IV  4.  Thus  in  three  separate 
instances  has  discovery  justified  in  the  most  striking  man- 
ner the  faith  of  Mendeleeff,  that  he  had  formulated  a  great 
and  fundamental  truth  of  nature.  And  it  is  interesting 
to  note  the  three  nationalities  which,  in  the  commemorative 


236        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

names  of  the  three  elements,  bear  witness  to  the  brilliant 
discovery  of  a  Eussian.  An  analogous  discovery  in  astron- 
omy affords  an  interesting  comparison.  Based  upon  ob- 
served peculiarities  in  the  motion  of  the  outermost  planet 
of  the  solar  system  as  known  at  that  time — namely,  the 
planet  Uranus — the  French  astronomer,  Leverrier,  and  an 
Englishman,  Adams,  concluded  that  there  must  be  a  planet 
outside  of  Uranus,  and  they  calculated  its  probable  position 
at  a  specified  time.  Their  surmise  and  calculations  were 
verified  shortly  afterward  by  the  discovery,  in  1846,  of  the 
planet  Neptune  by  Galle,  of  Berlin,  in  the  position  indi- 
cated by  the  calculations. 

639  Mendeleeff  at  a  more  recent  date  (1889)  has  said :  "  I 
foresee  some  more  new  elements,  but  not  with  the  same 
certitude  as  before,"  and  he  describes  a  possible  element 
for  the  place,  VI  10  (Principles  of  Chemistry,  vol.  ii,  p. 
447).     Much  interest,  too,  would  attach  to  an  element  for 
the  place,  VII  5.     Naturally  the  discovery  of  a  new  ele- 
ment at  once  suggests  the  question,  Where  will  it  fit  in 
Mendeleeff's  scheme  ?    And  so,  concerning  the  more  re- 
cently discovered  elements,  argon,  helium,  and  neon,  there 
is  much  discussion  with  reference  to  this  matter  without 
as  yet,  it  must  be  said,  any  satisfactory  conclusion. 

640  Applications  of  periodicity, — The  notion  of    periodicity 
once  established,  it  is  applicable  in  determining  the  com- 
bining weight  from  the  experimentally  determined  equiva- 
lent weight.     Thus  in  the  instance  of  glucinum  the  rela- 
tion of  periodicity  was  urged  in  favor  of  the  combining 
weight,  9,  the  second  multiple  instead  of  13.5,  the  third 
multiple,  before  the  determination  of  the  specific  gravity 
of  the  gaseous  chloride  confirmed  the  choice  of  the  former. 
There  is  still  question  as  to  the  exact  combining  weight 
of  tellurium,  VI  6.     Its  periodic  relation  should  make  the 
value  less  than  that  of  iodine,  while  recent  determinations 
show  a  slightly  higher  value,  and  it  is  doubted  if  the  sub- 
stance in  hand  is  truly  elemental.     There  is  a  similar  ques- 


DESCRIPTION  OF   ELEMENTS  AND  COMPOUNDS    237 

tion  as  to  the  relative  order  of  nickel  and  cobalt,  VIII  3. 
Again,  new  and  more  accurate  determinations  of  the  com- 
bining weights  established  the  periodic -order  of  osmium, 
iridium,  platinum,  and  gold,  as  given  in  the  table,  whereas 
the  earlier  order  was  gold,  iridium,  platinum,  and  osmium. 

Conclusion. — Finally,  although  there  are  still  unsatisfac-  641 
tory  features  of  the  Mendeleeff  table  when  it  is  attempted 
to  include  all  the  elements,  particularly  among  those  of 
high  combining  weight  and  those  of  which  little  is  now 
known,  and  although  the  law  is  still  incompletely  and 
imperfectly  expressed,  it  may  nevertheless  be  fairly  claimed 
in  its  behalf  that  it  is  a  discovery  of  the  very  highest  order. 
This  claim  is  justified  by  the  broad  significance  of  the 
underlying  principle,  by  its  usefulness  in  testing  the  valid- 
ity of  conclusions,  by  its  revealing  otherwise  unrecognized 
relations,  and  by  its  fertility  of  suggestion.  As  Mendeleeff 
says,  a  true  law  of  nature  leads  to  improved  methods  of 
research,  anticipates  facts,  foretells  magnitudes,  gives  a 
hold  on  nature  (Principles  of  Chemistry,  vol.  ii,  p.  26). 


AFTEBWORD 


642         THE  starting  point  of  this  brief  course  was  the  simple 
observation  that  the  things  about  us  are  not  permanent  but 
changeful.     In  your  developing  experience  you  have  seen 
these  changes  grow  bewilderingly  numerous  and  varied. 
Then,  deepening  penetration  has  shown  all  their  complexity 
resolved  into  the  simpler  changes — namely,  the  combina- 
tions and  recombinations  of  the  elemental  forms  of  matter. 
Looking  still  further  into  the  nature  of  these  changes,  you 
have  seen  that  they  are  subject  to  simple  laws  of  quantity, 
as  a  consequence  of  which  they  manifest  themselves  always 
associated  in  a  peculiar  manner  with  certain  definite  masses 
of  matter.    Next,  one  phenomenon  after  another,  seemingly 
of  most  diverse  nature,  has  been  brought  into  close  relation 
with  these  same  definite  masses.     The  following  step  ex- 
tended the  range  of  your  experience  and  brought  you  to  a 
closer  acquaintance  with  a  few  of  the  innumerable  and 
varied  kinds  of  matter.     And,  finally,  these,  in  spite  of  their 
multiplicity  and  variety,  are  brought  into  orderly  relation 
with  the  same  definite  masses.     And  thus  that  which  other- 
wise would  be  chaotic  and  meaningless  reveals  itself  to  you 
as  the  order  and    symmetry  of  intelligence   manifest  in 
things.     What  you  have  seen  and  heard  is  but  a  fragment ; 

vastly  more   remains  untold  and  yet  more  undiscovered. 

238 


AFTERWORD  239 

But,  now  at  the  end  of  the  course,  if  you  have  come  to 
realize  somewhat  better  than  before  the  beauty  and  signifi- 
cance of  the  physical  world  in  which  you  live,  and  have 
been  brought  into  closer  touch  with  the  great  nature  of 
which  you  form  a  part,  then  you  have  gained  something 
of  worth  which  will  stay  by  you  long  after  the  single  facts 
and  experiences  which  were  its  accompaniment  shall  have 
passed  from  your  minds. 


240        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


643 


TABLE  X. —  The  Elements  in  Alphabetical  Order 


No. 

NAME. 

Symbol. 

Combining 
weight.    H=l. 

Combining 
weight.    O=l  6. 

11 

Aluminium  .  .  . 

Al 

26  9 

27  1 

46 

Antimony 

Sb 

119  1 

120  0 

74 

Argon  

A 

19  8 

80 

Arsenic    

As 

74  4 

75  0 

50 

Barium  

Ba 

136  39 

137  4 

70 

Bismuth 

Bi  " 

206  5 

208  1 

4 

Boron  

B 

10  86 

10  95 

32 

Bromine  

Br 

79  35 

79  96 

43 

Cadmium  

Cd 

111  4 

112  2 

49 

Cassium      ... 

Cs 

131  9 

132  9 

17 

Calcium 

Ca 

39  7 

40  0 

5 

Carbon  

c 

11  91 

12  0 

5?, 

Cerium    

Ce 

139  0 

140  0 

15 

Chlorine 

Cl 

35  18 

35  45 

21 

Chromium  

Cr 

51.74 

52.14 

25 

Cobalt  

Co 

58.6 

59  0 

37 
26 

Columbium  or  niobium  .  .  . 
Copper  .  , 

Cb 
Cu 

93.0 
63.12 

94.0 
63.60 

58 

Erbium  

Er 

164.7 

166. 

8 

Fluorine  ... 

F 

18.91 

19.06 

56 

Gadolinium      

Gd 

155.6 

156.8 

28 

Gallium 

Ga 

69.4 

70.0 

29 

Germanium  '  

Ge 

71.9 

72.5 

3 
66 

Glucinum  or  beryllium  .  .  . 
Gold  

Gl 
Au 

9.0 
195.7 

9.1 
197.2 

73 

Helium 

He 

1.98 

1 

Hydrogen 

H 

1. 

1.008 

44 

Indium 

In 

113.0 

113.9 

47 

Iodine  

I 

125  89 

126.85 

64 

Iridium  

Ir 

191.6 

193.0 

23 

Iron  

Fe 

55.6 

56.0 

51 

Lanthanum  

La 

137.45 

138.5 

69 

Lead  

Pb 

205.34 

206.9 

9, 

Lithium  

Li 

6  97 

7.03 

10 

Magnesium 

M£ 

24  10 

24.28 

#>, 

Manganese 

Mn 

54  57 

55.0 

67 

Mercury  . 

Hz 

198.5 

200.0 

THE  ELEMENTS  IN  ALPHABETICAL  ORDER       241 


TABLE  X. — The  Elements  in  Alphabetical  Order  (continued] 


No. 

NAME. 

Symbol. 

Combining 
weight.     H  =  l. 

Combining 
weight.    O=16. 

33 

Molybdenum 

Mo 

95.3 

96  0 

54 

Neodymiurn  ,  

Nd 

142.5  (?) 

143.6(?) 

75 

Neon  

9.5 

24 

Nickel            

Ni 

58.24 

58.7 

6 

Nitrogen 

N 

13.93 

14  04 

63 

Osmium 

Os 

189  6 

191  0 

0 

15.88 

16.00 

41 

Palladium     

Pd 

105.6 

106.4 

13 

Phosphorus          .    •    . 

P 

30  8 

31  0 

65    ' 

Platinum 

Pt 

193  3 

194  8 

16 

Potassium 

K 

38  82 

39  11 

58 

Praseodymium  

Pr 

139  4  (1} 

140.5  (?) 

40 

Rhodium              .       ... 

Rh 

102  2 

103  0 

33 

Rubidium 

Rb 

84  78 

85  43 

39 

Ruthenium  

Ru 

100.9 

101.7 

55 

Samarium     

Sm 

149.     (?) 

150      (?) 

18 

Scandium         .        .... 

Sc 

43.8 

44  1 

31 

Selenium 

Se 

78.5 

79  1 

12 

Silicon                        . 

Si 

28  2 

28  4 

49 

Silver  

Ag 

107.11 

107.92 

9 

Sodium 

Na 

22.88 

23  05 

34 

Strontium                        .  . 

Sr 

86.95 

87  6 

14 

Sulphur  

S 

31.83 

32.07 

61 

Tantalum  

Ta 

181.6 

183.1 

48 

Tellurium 

Te 

126.5 

127.5 

57 

Terbium 

Tb 

158  8  (?) 

160      (?) 

68 

Thallium  

Tl 

202.6 

204.1 

71 

Thorium     

Th 

230.8 

232.6 

59 

Thulium 

Tu 

169.4  (?) 

170.7(?) 

45 

Tin 

Sn 

118  1 

119.0 

19 

Titanium  

Ti 

47.8 

48.1 

69 

Tungsten 

W 

183. 

184.4 

79 

Uranium 

u 

237  8 

239.6 

90 

Vanadium 

V 

51  0 

51.4 

60 

Yt 

171.7 

173. 

35 

Yttrium      

Y 

88.3 

89.0 

97 

Zinc  

Zn 

64.9 

65.4 

36 

Zirconium  . 

Zr 

89.7 

90.4 

242        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


644 


TABLE  XI. — The  Elements  in  Natural  Order 


No. 

NAME. 

Symbol. 

Equivalent 
weight. 

Fac- 
tor. 

Combining 
weight.* 
H  =  l. 

Combin- 
ing wt.* 
0  =  16. 

1 

Hydrogen     .    .  . 

H 

1. 

1 

1. 

1.008 

9 

Lithium  

Li 

6.97 

1 

6.97 

7.03 

3 

4 
5 
6 

Glucinum  or 
beryllium  
Boron  
Carbon  
Nitrogen   

Gl 
B 
C 

N 

4.5 
3.62 
2.9775 
4.  §43 

2 
3 
4 
3 

9.0 
10.86 
11.91 
13.93 

9.1 
10.95 
12.00 
14.04 

7 

Oxygen 

0 

7.94 

2 

15.88 

16.00 

8 

Fluorine  

F 

18.91 

1 

18.91 

19.06 

9 

Sodium 

Na 

22.88 

1 

22.88 

23.05 

10 
11 
12 

Magnesium  
Aluminium  .... 
Silicon  

Mg 
Al 
Si 

12.05 
8.967 
7.05 

2 
3 
4 

24.10 
26.9 

28.2 

24.28 
27.1 

28.4 

13 

14 

Phosphorus  .... 
Sulphur 

P 

S 

10.267 
15.91 

3 

2 

30.8 
31.83 

31.0 
32.07 

15 

Chlorine 

Cl 

35.18 

1 

35.18 

35  .  45 

16 
17 

Potassium  
Calcium  

K 
Ca 

38.82 
19.9 

1 
2 

38.82 
39.7 

39.11 
40.0 

18 

Scandium  

Sc 

14.6 

3 

43.8 

44.1 

19 

Titanium 

Ti 

11  95 

4 

47  8 

48  1 

90 

Vanadium 

V 

17.0 

3 

51.0 

51  4 

21 
22 
9,3 

Chromium  ...    . 
Manganese  
Iron 

Cr 
Mn 
Fe 

17.25 

27.28 
27  80 

3 

2 
2 

51.74 
54.57 
55  6 

52.14 
55.0 
56  0 

94 

Nickel    .    .     . 

Ni 

29  12 

2 

58  24 

58  7 

9,5 

Cobalt  

Co 

29  3 

2 

58  6 

59  0 

96 

Cu 

31  56 

2 

63  12 

63  60 

97 

Zinc 

Zn 

32  45 

o 

64  0 

65  4 

98 

Gallium 

Ga 

23  13 

3 

69  4 

70  0 

29 
30 

Germanium  .... 
Arsenic  

Ge 

As 

17.975 

24  8 

4 
3 

71.9 

74  4 

72.5 

75  0 

31 
39 

Selenium  
Bromine 

Se 
Br 

39.2 
79  35 

2 

1 

.     78.5 
79  35 

79.1 
79  96 

33 

Rubidium 

Rb 

84  78 

1 

84  78 

85  43 

34 

35 

Strontium  
Yttrium  

Sr 
Y 

43.47 
29.4 

•  2 
3 

86.95 

88.3 

87.6 
89.0 

36 

Zirconium  

Zr 

22.43 

4 

89.7 

90.4 

*  According  to  Clarke,  Journal  of  the  American  Chemical  Society, 
xxi,  213,  February,  1899 ;  and  Richards,  American  Chemical  Journal, 
xx,  543  (July,  1898). 


THE  ELEMENTS  IN  NATURAL  ORDER 


243 


TABLE  XL — The  Elements  in  Natural  Order  (continued) 


No. 

NAME. 

Symbol. 

Equivalent 
weight. 

Fac- 
tor. 

Combining 
weight. 

Combin- 
ing wt. 
O-=  16. 

37 

Columbium     or 
niobium 

Cb 

31. 

3 

93 

94  0 

38 
39 
40 

Molybdenum  .  .  . 
Ruthenium  
Rhodium  

Mo 
Ru 
Rh 

47.6 
50.45 
51.1 

2 
2 
2 

95.3 
100.9 
102.2 

96.0 
101.7 
103  0 

41 

Palladium 

Pd 

52  8 

2 

105  6 

106  4 

42 

Silver 

107  11 

1 

107  11 

107  92 

43 

44 

Cadmium  
Indium 

Cd 
In 

55.7 
37  67 

2 
3 

111.4 
113  0 

112.2 
113  9 

45 

Tin 

Sn 

29  5 

4 

118  1 

119  0 

46 

Antimony 

Sb 

39  7 

3 

119  1 

120  0 

47 

Iodine 

I 

125  89 

1 

125  89 

126  85 

48 

Tellurium  

Te 

63.25 

2 

126.5 

127.5 

49 

Cassium  

Cs 

131.9 

1 

131.9 

132.9 

50 

Barium  

Ba 

68.20 

2 

136.39 

137.4 

51 
59. 

Lanthanum  .... 
Cerium  

La 
Ce 

45.81 
34.75 

3 
4 

137.45 
139.0 

138.5 
140.0 

53 
54 
55 

Praseodymium.  . 
Neodymium  
Samarium 

Pr 

Nd 
Sm 

.     46.5 
47.5 
49.7 

3 

139.4(?) 
M49.    (?) 

140.  5(?) 
143.6(1) 
150.   (?) 

56 
57 

Gadolinium  .    .  . 
Terbium          .  .  . 

Gd 
Tb 

51.87 
52  93 

3 
3 

155.6  (?) 

158  8  (?) 

156.  8(?) 
160.  (?) 

58 

Erbium 

Er 

54.9 

3 

164.7  (?) 

166.  (?) 

59 

Thulium 

Tu 

56  5 

3 

169.4  (?) 

170.7(1) 

60 

Ytterbium 

Yt 

57  2 

3 

171.7  (?) 

173.  (?) 

61 

Tantalum 

Ta 

36  3 

5 

181.6 

183. 

69 

Tungsten  .  . 

W 

91  5 

2 

183.0 

184.4 

63 

Osmium            .  . 

Os 

47  4 

4 

189.6 

191.0 

64 

Iridium 

Ir 

47.9 

4 

191.6 

193.0 

65 

Platinum    ...    . 

Pt 

48.33 

4 

193.3 

194.8 

66 

Gold       

Au 

195.7 

1 

195.7 

197.2 

67 

Mercury 

Hg 

99  25 

2 

198.5 

200.0 

68 

Thallium  

Tl 

67.51 

3 

202.6 

204.1 

69 

Lead  .  . 

Pb 

102.67 

2 

205.34 

206.9 

70 

Bismuth 

Bi 

68.83 

3 

206.5 

208.1 

71 

Thorium  

Th 

57.7 

4 

230.8 

232.6 

72 

IT 

59.45 

4 

237.8 

239.6 

73 

Helium 

He 

74 

Argon  ...    .  /.  .  . 

A 

19.8  (?) 

75 

Neon  

9.5  (?) 

17 


INDEX 


The  references  are  to  marginal  numbers.  Part  II  is  designated  by  the  Roman 
numeral,  and  the  appendix  by  the  abbreviation  Ap.  The  numbers  are  the  same 
for  the  same  topics  in  Parts  I  and  II. 


Acetylene,  280,  281/2. 
Acid  defined,  30/V 

boric,  225. 

carbonic,  264. 

chloric,  541. 

chlorous,  541. 

hydrazoic,  343. 

hydrochloric,  533-535. 

hydrofluoric,  405,  406. 

hydrosulphuric,  510-512. 

hypochlorous,  538. 

hyponitrous,  314. 

nitric,  326-332. 

nitrohydrochloric,  331/2,  II. 

nitrous,  320. 

perchloric,  541. 

phosphoric,  494,  495. 

phosphorous,  493. 

salt  defined,  30/6. 

silicic,  473,  474. 

sulphuric,  519-526. 

sulphurous,  516. 

thiosulphuric,  522. 
Additive  combination,  441. 
Additive  compound  denned,  336. 
Air,  338-395. 
Alkalies  defined,  215. 
Allotropic  change  defined,  13. 
Alloy  defined,  456. 
Alum,  461/j. 


Aluminium,  448-465. 

manufacture  of,  462-465. 
Ammonia,  334-338. 

compounds,  336,  337. 
Amorphous  defined,  21/6. 
Analytic  reaction  defined,  81. 
Anhydrite,  578. 
Anhydrous  defined,  21/7. 
Anthracitic  diamond,  240. 
Apatite,  485. 
Argon,  396. 
Arrhenius,  176. 
Asbestos,  443. 
Asymmetric  defined,  185. 
Atmosphere,  388-395.        «**  ; 
Atom  defined,  171. 
Atomic  theory,  40/6,  157-186. 
Atomic  weights  defined,  173. 
Atoms,  heat  capacity  of,  175. 
Avogadro's  hypothesis,  165. 
Azote.     See  Nitrogen,  306. 

Bacteria  in  nitrification,  328. 

in  water,  377. 
Balances,  Ap.  1. 
Barometer,  Ap.  15  B. 
Base  defined,  30/2. 
Basic  salt  defined,  30/6. 
Basicity  of  acids,  table,  Ap.  23. 
Bauxite,  449. 

245 


246        ELBMBNTAKY  PRINCIPLES  OF  CHEMISTRY 


Bending  glass  tube,  Ap.  9. 

Benzene,  282. 

Bergmann,  259. 

Berthollet,  37/6. 

Beryllium.  See  Glucinum,  216-219. 

Berzelius,  466. 

Black,  259,  577. 

Blasting  gelatin,  575. 

Bleaching  powder,  547,  548. 

Blowpipe,  use  of,  Ap.  21. 

Boiling  denned,  11. 

Boiling  point  affected,  24/l5  24/2. 

apparatus,  Ap.  17. 

denned,  24. 

Boiling  temperature,  constant  of 
elevation,  130. 

constants,  tables,  132-135. 

determination  of,  127/j,  127/3, 
II. 

molecular  elevation  of,  176. 

specific  elevation  of,  126. 
Bone  black,  252. 
Borax,  228. 

bead,  228,  II. 
Boric  acid,  225. 
Boron,  220-228. 
Boyle,  66/3,  388. 
Boyle's  Law,  66. 

apparatus  for,  66,  II. 
Brand,  484. 

Brimstone.     See  Sulphur. 
Bromine,  541/j. 
Bumping,  24/2. 
Bunsen,  450. 
Butane,  278. 
Butylene,  279. 

Calcium,  577-584. 
Calorie  denned,  50A,  II. 

•v'      ?^»-_ 


Carbon,  234-258. 
amorphous,  248-258. 


Carbon,  gas,  251. 

Carbon  as  constituent,  247. 

dioxide,  259-268. 

dioxide,  weight  of  one  liter  de- 
termined, 81/x,  81/2,  II. 

monoxide,  272,  273. 
Carbonado,  240. 
Carbonates,  265,  269-271. 
Carbonic  acid,  264. 
Carborundum,  258. 
Cavendish,  200,  326,  368,  388. 
Charcoal,  252,  254. 
Charles's  Law,  67-67/4. 

apparatus,  67,  II. 
Chemical  properties  defined,  3. 

change,     essential    feature    of, 
13. 

change,  secondary  features,  14. 
Chemism,  51. 
Chemistry  defined,  2. 
Chromite,  594. 
Chromium,  592-606. 
Chlorine,  527-532. 

manufacture,  54%-54"6. 

oxides,  536-540. 
Chloric  acid.  541. 
Chlorous  acid,  541. 
Chlorophyll,  266. 
Classification,  early,  621,  622. 
Coal,  298-300. 
Coal  gas,  301,  302. 
Cobalt,  592-606. 
Coefficient  of  expansion,  67,  II. 
Coke,  253. 

Combining   weights   of    elements, 
defined,  44,  45. 

determination  of,  150-152. 

list  of,  643,  644. 

weights    of    compounds,   deter- 
mination of,  155. 

weights,  system  of,  61. 
Combustion,  34/4,  II,  354. 


INDEX 


247 


Combustion  of  sulphur,  13,  II. 
Composition  defined,  15. 
Compound  defined,  27. 
Congelation  defined,  10. 
Cooke,  623. 
Cordite,  576. 
Corundum,  449. 
Crookes,  Sir  William,  348. 
Cryolite,  401. 
Crystallization,  21/4. 

water  of,  21/7. 
Cutting  glass  tube,  Ap.  7. 

Dalton,  40,  159,  174. 

Dalton's  Law  (Charles's  Law),  67/2. 

Data,  table,  Ap.  22. 

Davy,  Sir  Humphry,  220,  235,  407, 
442,  527,  549,  577. 

Decanting  defined,  18/B,  II. 

Decomposition  defined  and  illus- 
trated, 16. 

D%epitation,  !Q/lt  II. 

Dehy^ed  defined,  21/7. 

Deli^uesc^e^^efined,  21/8. 

Destructive   crafcyilation   of   wood, 
303-305. 

Deville,  450. 

Dewar,  206,  395,  404. 

Diamond,  235-241. 
artificial,  241. 

Diffusibility,  law  of,  203/V 

Dimorphous  defined,  21/6. 

Dissociation,    electrolytic,    theory 
of,  176. 

Distillate  defined,  12. 

Distillation  defined,  12. 

Distilling  apparatus,  Ap.  18. 

Dolomite,  443. 

Dorcet,  235. 

Dulong,  339. 

Dulong  and  Petit,  100. 
law  of,  95-106. 


Dumas,  621,  623. 

Dynamic  chemistry  defined,  26. 

Dynamite,  572. 

Ebullition  defined,  11. 
Effervescence  defined,  13/j  (6),  II. 
Efflorescent  defined,  21/8. 
Electric  furnace,  241. 
Electrolysis  defined,  202. 
Electrolytic     dissociation    theory, 

176. 

Element  defined,  27. 
Elements,  free  or  combined  in  na- 
ture, 192. 

in  the  living  organism,  191. 
list  of,  643,  644. 
metallic,  193. 
non-metallic,  193. 
their  chemical  activity,  198. 
their  distribution,  189. 
their  oxidation  heat,  its  range, 

199. 
their    range    in    boiling    point, 

195. 

their  range  in  density,  196. 
their  relative  quantity,  190. 
Energy,  chemical,  familiar  forms, 

60. 

chemical  and  electric,  59. 
defined,  1. 
persistence  or  conservation    of, 

34/9. 

persistence   or   conservation  of, 
in  chemical  phenomena,  50-60. 
Endothermic  defined,  54. 
Epsom  salt,  443. 
Equations,  63-63/2. 
Equivalent    proportions,    law    of, 

41-46. 

weight  defined,  42-44. 
weights,  accuracy  of,  145-148. 
weights,  basis  of,  146. 


248        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


Equivalent  weights,  determination 

of,  142-149. 

weights,  list  of,  643,  644. 
Ethane,  278. 
Ethylene,  279. 

Evaporating  to  dryness,  Ap.  12. 
Evaporation  defined,  11. 
Exchange,  double,  18. 
Exothermic  defined,  54. 
Explosives,  555-576. 

Factors  defined,  26. 

Feldspar,  482. 

Fertilizers  (phosphates),  502. 

Filtration,  filtrate  defined,  18  A  (c), 

II. 
Filtration,  the  manipulation,  Ap. 

13. 
Fixed  proportions,  the  law  of,  37- 

37/8. 

Flame,  nature  of,  284-292,  II. 
Fluor  spar,  401. 
Fluorine,  401-406. 
Fluorite,  401. 

Formula  of  compounds,  determi- 
nation, 153-155. 
Fornmla  weight,  62/^. 
Freezing  defined,  10. 
Freezing  point  defined,  23. 
constants  of  depression,  117. 
constants  of    depression,   table, 

120-123. 

depression  of,  23/i. 
molecular  depression  of,  176. 
specific  depression  of,  110/B. 
specific  depression  of,  determi- 
nation, 111/, .-111/4,  II. 
Fusion  defined,  10. 

Gallium,  638. 

Galvanic  cell,  59. 

Gas,  manipulation  of,  A  p.  19. 


Gas,  volumetric  proportions,  47- 

47/7. 

Gases,  kinetic  theory  of,  164. 
Gases,  volume,  pressure,  and  tem- 
perature, 66-67/4. 
Gay-Lussac,  47/7,  89,  220. 
Gay-Lussac's  Law  (specific  gravi- 
ties), 71-94. 

see  Charles's  Law,  67/2. 

(volumetric  proportions),  47. 
Generator,  gas,  A  p.  6. 
Germanium,  638. 
Gladstone,  625. 
Glass,  477-481. 

soluble,  476. 
Glucinum,  216-219. 
Graduated  cylinder,  Ap.  14. 
Graphite,  243-246. 
Guano,  502. 
Guncotton,  573-576. 
Gunpowder,  556-564. 
Gypsum,  507,  578. 
_>• 

Halogens  defined.  541/i. 
Hardness  of  water,  375-375/3. 
Heat  capacity  of  atoms,  175. 
Heat  disturbance,  50. 
Heat  of  formation  defined,  53. 
Heat,  measurement  of,  54,  55,  55/j . 

of  neutralization,  50/4,  II. 

summation,  law  of,  55. 

unit  of,  defined,  50A,  II. 
Heats  of  formation,  list,  57. 
Heating  a  crucible,  Ap.  11. 

a  test-tube,  Ap.  2. 
Helium,  400. 
Helmholtz,  50,  note. 
Hematite,  594. 
Hess,  55. 

Homologous  defined,  278. 
Humboldt,  47/7. 
Hydrazine,  341. 


INDEX 


249 


Hydrazoic  acid,  343. 
Hydrocarbons,  274-283. 
Hydrochloric  acid,  533-535. 
Hydrofluoric  acid,  405-406. 
Hydrogen,  200-209. 

dioxide,  366,  367. 

peroxide,  366,  367. 
Hydrosulphuric  acid,  510-512. 
Hydroxylamine,  342. 
Hygroscopic  defined,  21  /8. 
Hypochlorous  acid,  538. 
Hyponitrous  acid,  314. 
Hyposulphite.     See  Thiosulphate, 
522. 

Increment  of  volume,  67,  II. 
Interaction  defined,  26. 
Iodine,  541A. 
lonization,  176. 
Iron,  592-606. 

commercial,  607-619. 
Isomerism,  stereo  or  physical,  183- 

185. 

Isomers  defined,  179. 
Isomorphous  defined,  21/6. 

Joule,  50,  note. 

Kaolin,  482. 

Kelvin,  Lord,  162. 

Kinetic  theory  of  gases,  164. 

Kopp  and  Neumann,  law  of,  103, 

104. 
Krypton,  399. 

Lake  (as  to  dyeing)  defined,  460. 

Lampblack,  250. 

Lavoisier,  34/B,  37/6,  200,  235,  259, 

306,  326,  388. 
Le  Bel,  185. 

Lecoq  de  Boisbaudran,  638. 
Lime,  581-583. 


Lime,  hydraulic,  587. 

preparation,  585. 
Limonite,  594. 
Lithium,  210-214. 

Magnesite,  443. 

Magnesium,  442-447. 

Magnetite,  594. 

Manganese,  592-606. 

Mariotte,  66/3. 

Marsh-gas.    See  Methane,  275-277. 

Mass  defined,  34. 

persistence   or  conservation   of, 

34/6- 

Matches,  505. 
Matter  defined,  1. 
Mayer,  J.  A.,  50,  note. 
Melting  defined,  10. 
Melting-point  apparatus,  Ap.  16. 

defined,  23. 

Mendeleeff,  625,  638,  639,  641. 
Metal  defined,  29. 
Metallurgy  defined,  257. 
Metamers  defined,  180. 
Metargon,  399. 

Metathetic  reaction  defined,  31. 
Methane,  275-277. 
Meyer,  Lothar,  625. 
Mitscherlich,  108. 

Law  of,  107,  108. 
Mixture  defined,  28.  . 
Moissan,  223,  241,  256,  401,  579, 

580. 
Molecular  depression  of  freezing 

point,  176. 

Molecular  elevation  of  boiling  tem- 
perature, 176. 
Molecular  theory,  160-163. 

weights  defined,  167. 
Molecule  defined,  166. 

of  compounds,  divisible,  168. 

of  elements,  divisible,  160,  170: 


250        ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


Molecules,  estimated  size,  162. 

structure  of,  177-182. 
Monobasic  defined,  333. 
Mordant  (as  to  dyeing)  defined,  460. 
Morley,  147. 
Mortar,  586. 

Mortar  and  pestle,  Ap.  5. 
Multiple  proportions,  law  of,  40- 
40/8. 

Nascent  state  defined,  208. 

theoretic  explanation  of,  208/2. 
Neon,  398. 

Neumann.     See  Kopp. 
Neutral,  neutralized  defined,  30/4. 
Neutralization,  heat  of,  50/4,  II. 
Neutralizing,  the  operation  of,  37, 

II. 

Newlands,  625. 
Nickel,  592-606. 
Nilson,  638. 
Nitrates,  333. 
Nitric  acid,  326-332. 
Nitric  oxide.   See  Dioxide,  317, 318. 
Nitrides,  340. 
Nitrification,  328. 
Nitrogen,  306-311. 

chloride,  339. 

dioxide,  317,  318. 

monoxide,  312-316. 

oxides1^  311. 

pentoxide,  325. 

peroxide,  323. 

tetroxide,  322-324. 

trioxide,  319-321. 
Nitroglycerine,  569-572. 
Nitrohydrochloric  acid,  331/2,  II. 
Nitrous  acid,  320. 
Nitrous  oxide.    See  Monoxide,  312- 

316. 

Nomenclature,  65-65/c. 
Non-metal,  29. 


Normal  salt  defined,  30/6. 
Notation  for  compounds,  62-62/2. 

for\elements,  62. 

preliminary  statement,  19,  II. 

Occlusion  defined,  205. 

Octaves,  law  of,  625. 

Olefins,  279. 

Organic  chemistry  defined,  283. 

Oxidation  (as  to  valence),  441/». 

Oxides,  classes  of,  355. 

Oxidizing  agents  defined,  48,  II. 

flame,  Ap.  21. 
Oxygen,  350-357. 

weight  of  one  liter,  71  A,  II. 
Ozone,  358-365. 

Paracelsus,  200. 
Paraffins,  278. 
Pasteur,  184. 
Perchloric  acid,  541. 
Periodicity,  589,  620,  625,  640. 
Permanganate,  604. 
Pestle  and  mortar,  Ap.  5. 
Petit.    See  Dulong. 
Petroleum,  293-297. 
Phosphine,  496. 
Phosphoric  acid,  494,  495. 
Phosphorous  acid,  493. 
Phosphorus,  484-501. 

manufacture,  498-501. 
Physical  isomerism,  183-185. 

properties  defined,  3. 

properties  enumerated,  4-12. 
Physico-chemical    properties    de- 
fined, 3. 
Physics  defined,  2. 
Plaster  of  Paris,  588. 
-'olymerization  defined,  281/2. 
5olymers  defined,  179. 
polymorphous  defined,  21/6. 
'orcelain,  482. 


INDEX 


251 


Potassium,  549-554. 

Pouring  from  reagent  bottle,  Ap.  3. 

Precipitate,  precipitation  defined, 

18/C,  II. 

Priestley,  306,  312,  334,  350,  388. 
Products  defined,  26. 
Propane,  278. 
Propylene,  279. 

Protoplasm,  its  composition,  191. 
Proust,  37/6,  40. 
Prout's  hypothesis,  624. 
Proximate  analysis  defined,  26. 
Pyrites,  507,  594. 
Pyrolusite,  594. 

Qualitative  analysis  defined,  26. 
Quantitative  analysis  defined,  26. 

Ramsay,  396,  398-400. 
Raoult,  law  of   (boiling  tempera- 
ture), 124-135. 

(freezing  point),  109-123. 
Rayleigh,  Lord,  396. 
Reactions  classified,  31. 

defined,  26. 
Reducing  agents  defined,  48,  II. 

flame,  Ap.  21. 

Reduction  (as  to  valence),  441/a. 
Richter,  40,  41/9. 
Ruby,  449. 
Rutherford,  306. 

Salt  defined,  30/3. 

Sapphire,  449. 

Saturated  defined  (as  to  valence), 

441. 
Saturation  defined  (as  to  solution), 

21/3- 

Scandium,  638. 

Scheele,  350,  484,  527. 

Siderite,  594. 

Silicates,  some  uses  of,  476-483. 


Silicic  acid,  473,  474. 
Silicon,  466-475. 
Soapstone.  443. 
Sodium,  407-410. 

carbonate,  413. 

chloride,  411,  412. 

hydroxide,  419,  420. 
Solubility  of  salts,  list,  Ap.  24. 
Solute  defined,  21. 
Solution  defined,  21. 

heat  of,  22. 
Solvent  defined,  21. 
Specific     depression    of    freezing 
point  defined,  110/a. 

determination,  lll/i-111/4,  II. 
Specific  elevation  of  boiling  tem- 
perature defined,  126. 

determination,  127/1-127/5,  II. 
Specific  gravity  defined,  7. 

determination,  8. 
Specific  heat  defined, 

of  compounds,  1 

determination,  95/2,  95/3,  II. 

of  elements,  table,  105. 

law  of,  95-106. 
Stas,  145. 

Static  chemistry  defined,  26. 
Steel,  607. 

Stereo-isomerism,  183-185. 
Stoichiometry,  64,  64/j. 
Stoneware,  483. 

Structure  of  molecules,  177-182. 
Sublimate,    sublimation,    defined, 

12. 

Substances  defined,  1. 
Substitution  defined,  17,  31. 
Sulphur,  507-509/4. 

oxides,  514-518. 
Sulphuric  acid,  519-526. 
Sulphurous  acid,  516. 
Superphosphate,  503. 
Surfusion,  23. 


252       ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


Survey,    general,    first    nine    ele- 
ments, 422-433. 

general,  seventeen  elements,  589, 
590. 

Synthetic  reaction  defined,  31. 

System,  chemical,  defined,  26. 

Talc,  443. 

Thenard,  220. 

Theory,  atomic,  157-186. 

of      electrolytic       dissociation, 
176. 

kinetic,  of  gases,  164. 
Thermometer,  Ap.  15  A. 
Thiosulphuric  acid,  522. 
Toluene,  282. 

Ultimate  analysis  defined,  26. 

Valence,  434-441 /.. 
Van't  Hoff,  185. 
Vapor-densities,  table,  93,  94. 


Vapor-density,     data,    discussion, 
72-87. 

defined,  71. 

determination,  71/A,  71/x,  II. 

effect  of  temperature  on,  88,  89. 

law  of,  71-94. 
Volumetric  proportions,  47-47/7. 

Water,  368-370. 

action  on  lead  and  zinc,  387. 

for  drinking,  377-377/5. 

purification  of,  378-386. 
Waters,  natural,  371-377/6. 
Weighing,  Ap.  1. 
Weights,  Ap.  1. 
Wenzel,  41/9. 
Winkler,  638. 
Wohler,  178,  216,  450. 
Wood,  destructive  distillation  of, 
303-305. 

Xenon,  399. 


PART    II 

EXPERIMENTAL  ILLUSTRATIONS 


KECOMMENDATIONS   AS   TO   NOTES 


THE  making  of  notes  is  a  very  important  item  in  the 
study  of  a  subject  in  the  laboratory.  The  student  should 
early  in  his  course  form  the  habit  of  writing  them  care- 
fully, thoughtfully,  and  systematically.  The  aim  should 
be  to  describe  the  essential  features  of  method  and  of  appa- 
ratus, then  the  things  observed,  then  the  things  learned 
from  the  experiment;  for  every  experiment  is  designed 
to  teach  something.  The  aim  should  also  be  to  make  the 
description  clear,  exact,  and  simple.  The  following  details 
of  plan  are  recommended :  To  use  a  book  about  six  by  nine 
inches  in  size,  one  whose  leaves  will  lie  flat  when  opened, 
with  plain,  unruled  pages  ;  to  enter  notes  only  on  the  right- 
hand  page,  leaving  the  left-hand  for  topics,  corrections,  ad- 
ditions, and  the  numerical  work  of  calculations ;  to  enter 
always  the  particular  topic  which  the  experiment  is  to  illus- 
trate ;  as  a  minor  item,  to  enter  the  date  of  work ;  for  con- 
venience, to  have  the  name  of  the  owner  on  the  outside  of 
the  cover.  The  notes  should  be  written  in  final  form  in 
the  laboratory,  and  not  copied. 

It  is  particularly  urged  that  the  student  should  read 
through  the  directions  for  an  experiment  before  starting 
upon  its  performance,  and  that  the  experiment  should  pre- 
cede the  consideration  of  the  corresponding  topic  in  Part  I. 


THE   ELEMENTARY   PRINCIPLES 
OF   CHEMISTRY 


PART    II 

EXPERIMENTAL  ILLUSTRATIONS    • 
CHAPTER   I 

INTRODUCTION 

Read  Part  I,  Nos.  1-6,  before  beginning  the  experiments. 
1.  Physical  Properties  of  Sulphur 

Observe  as  to  odor,  color,  hardness,  form  (crystalline   1-6* 
— that  is,  regular  geometric  form). 

To   determine  its  specific  gravity:  Weigh   carefully   to   7 
tenths  about  10  grams  of  dry  sulphur,  in  small  lumps,  free 
of  dust.     Weigh  a  test-tube,  filled  with  water  and  corked. 
Put  the  sulphur  in  the  test-tube,  refill  with  water,  cork, 
and  weigh  (see  Appendix,  1). 

The  specific  gravity  of  sulphur  equals  the  weight  of 
sulphur  divided  by  the  weight  of  an  equal  volume  of  water. 
Calculate  the  specific  gravity  from  the  observations  made. 

Suggest  another  method  for  solids ;  also  one  suitable  for  solids    8 
which  are  soluble  in  water ;  a  method  for  liquids ;  for  gases. 

Electrification. — Rub  a  large  lump  briskly  on  the   dry  9 
towel,  or,  better,  on  some  woolen  stuff.     It  becomes  electri- 
fied and  capable  of  attracting  particles,  like  bits  of  paper. 

*  The  marginal  numbers  are  the  same  for  the  same  topics  in  both 
Part  I  and  Part  II. 

1 


V2  ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

10  Effects  of  heating. — Heat  in  a  dry  test-tube  some  lumps 
of  dry  sulphur,  the  test-tube  being  about  half  filled.  It  is 
well  to  make  a  holder  by  folding  a  strip  of  paper  once  or 
twice  upon  itself,  to  wrap  this  about  the  test-tube  and  to 
seize  the  ends  close  to  the  tube  with  the  fingers,  or;  better, 
with  the  tongs  (see  Appendix,  2).  Apply  the  heat  grad- 
ually by  passing  the  tube  slowly  back  and  forth  through  the 
flame.  Have  a  vessel  filled  with  water  on  the  table  close  at 
hand.  Should  the  tube  crack  and  the  sulphur  take  fire, 
hold  quickly  over  the  water.  Let  the  temperature  rise 
slowly  while  the  sulphur  is  melting.  2s  ote  the  color.  Keep 
the  surface  of  the  liquid  in  gentle  motion  ;  note  the  partial 
1 1-12  solidification.  Continuing  the  heat,  note  the  second  lique- 
faction, the  beginning  of  boiling,  and  the  white  dustlike 
deposit  (sublimate).  Now,  as  the  sulphur  is  beginning  to 
boil,  move  the  burner  to  one  side  ;  carefully  and  slowly  turn 
the  melted  sulphur  into  the  water,  moving  the  tube  to  and 
fro  so  as  to  string  it  out.  Set  aside  the  tube  with  the  small 
residue  of  sulphur  and  observe  it  from  time  to  time  as  it 
cools  (solidification  and  crystallization}.  Examine  the  por- 
tion which  has  been  suddenly  cooled  in  the  water  (allotro- 
pism),  comparing  it  with  the  original.  Select  a  good  sample 
of  it,  and,  without  lumping  it  together,  dry  it  by  pressing 
and  rubbing  first  between  folds  of  the  towel,  then  between 
absorbent  papers  (filter  papers).  Weigh  the  sample  care- 
fully and  leave  it  for  twenty-four  hours.  Does  it  change  in 
weight  in  passing  from  the  plastic  amorphous  (see  Part  I, 
No.  21/6 )  to  the  brittle  crystalline  form  ? 

12/1  Crystallization  from  fusion  (see  No.  21/4  ,  Part  I). — Fuse  some  dry 
sulphur  in  a  crucible,  keeping  the  temperature  as  low  as  will  suffice  to 
melt ;  let  it  cool  slowly  until  a  crust  has  formed ;  puncture  the  crust 
and  pour  out  the  remaining  liquid;  break  the  crucible  and  note  the 
appearance  of  the  crystals  known  as  monoclinic  sulphur ;  examine  them 
twenty-four  hours  later.  (It  is  recommended  that  the  instructor  do  this 
experiment  for  the  class.) 

12/2  Crystallization  from  solution  (see  No.  21/4 ,  Part  I). — Dissolve  some 
sulphur  in  carbon  disulphide  to  saturation,  or  nearly  so,  decant  (that  is, 


INTRODUCTION  3 

drain  off)  or  filter  the  liquid  and  allow  it  to  evaporate  in  the  hood. 
Examine  the  crystals  known  as  orthorhombic  sulphur ;  compare  with 
those  of  the  preceding  experiment  (dimorphism}.  Do  they  change  on 
standing  ?  As  carbon  disulphide  is  very  volatile  and  combustible,  great 
care  should  be  taken  to  have  no  flame  near.  (It  is  recommended  that 
the  instructor  do  this. experiment  for  the  class.) 

2.  Chemical  Properties  of  Sulphur 

Burning  or  combustion. — Ignite  a  small  lump  of  sulphur  13 
(half  the  size  of  a  pea)  on  a  suitable  surface  (an  earthen 
saucer  serves  well).  Describe  the  phenomenon.  The  gase- 
ous product  is  sulphur  dioxide  ;  observe  its  odor  cautiously, 
and  its  effect  on  litmus — conveniently  done  by  sticking  a 
piece  of  wet,  blue  litmus  paper  to  the  bottom  of  a  beaker 
and  inverting  the  latter  over  the  burning  sulphur.  Com- 
pare the  sulphur  dioxide  in  these  respects  with  the  sulphur. 
If  you  have  a  sample  of  the  plastic  sulphur,  burn  and  test 
this  in  the  same  manner. 

EXPLANATORY  NOTE. — An  invisible  gas,  namely,  oxygen,  a  constituent 
of  the  atmosphere,  takes  part  in  this  change,  combining  with  the  sulphur 
and  forming  the  sulphur  dioxide,  which  is  quite  different  from  both  the 
sulphur  and  the  oxygen. 

Behavior  with  zinc. — Weigh  out  carefully  3.20  grams  of  13/1 
finely  divided  sulphur  (sulphur  sublimate,  commonly  called 
sulphur  flowers) ;  also  6.50  grams  of  finely  divided  zinc 
(zinc  dust).  Mix  these  thoroughly  in  a  mortar,  so  that 
the  original  powders  can  not  be  distinguished  (see  Appen- 
dix, 5).  Take  out  a  small  portion,  about  as  much  as  could 
be  heaped  on  a  five-cent  piece  (putting  the  remainder  well 
to  one  side) ;  heat  this  strongly  on  the  earthen  saucer  or  on 
the  asbestos  board  by  turning  the  gas  flame  down  upon  it, 
or,  still  better,  on  the  spatula  blade  by  thrusting  it  into  the 
flame.  Do  this  cautiously,  as  it  may  flash  up  somewhat  like 
gunpowder.  In  experiments  like  this,  the  face  should  never 
be  held  over  the  material  Describe  the  phenomenon,  note 
the  ashlike  product,  compare  it  with  the  original  sub- 


4  ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

stances,  sulphur  and  zinc,  by  inspection.     Does  it  melt  and 
burn  like  sulphur  ? 

(a)  Put  a  little  of  the  mixed  powders  from  the  mortar 
in  a  test-tube,  half  fill  with  water,  then,  closing  the  tube 
with  the  thumb,  shake  it  vigorously,  and  finally  let  the 
powder  settle  (see  Appendix,  4).     Does  the  powder  dissolve  ? 
Do  you  see  the  sulphur  tend  to  separate  from  the  mixture 
with  the  zinc  ?    In  a  similar  manner  shake  some  of  the  ash- 
like  product  with  water.    Does  it  dissolve  ?    Do  you  see  any 
tendency  of  the  sulphur  to  separate  from  the  zinc  ?    Does 
zinc  dissolve  in  water  ?    Does  sulphur  dissolve  in  water  ? 

(b)  Put  a  small  quantity  of  the  ashlike  product  in  a 
test-tube  and  add  to  it  a  few  drops  of  hydrochloric  acid, 
better  designated  as  hydrogen  chloride  (see  Appendix,  3). 
Note  the  phenomenon  of  effervescence  (bubbles  of  gas  in  the 
liquid ;  how  does  it  differ  from  boiling  ?),  indicating  the 
formation  or  liberation  of  a  gas  not  previously  apparent. 
Note  the  odor  of  this  gas  (with  care,  for  the  substance  is  very 
poisonous)  and  its  effect  on  a  bit  of  filter  paper  wet  with  a 
solution  of  lead  acetate,  and  held  at  the  mouth  of  the  test- 
tube.     Does  the  ashlike  product  disappear  in  the  acid  ?    If 
not,  warm  the  tube  slightly. 

Compare  this  with  the  behavior  of  a  little  zinc  treated 
in  another  test-tube  with  hydrogen  chloride  in  a  similar 
way  (does  the  zinc  powder  disappear  ?) ;  also  of  sulphur 
thus  treated  ;  also  of  the  mixed  zinc  and  sulphur  (does  this 
powder  disappear  ?). 

EXPLANATORY  NOTE. — In  this  experiment  you  have  brought  about  a 
chemical  change.  Starting  with  zinc  and  sulphur,  mixing  them  inti- 
mately and  applying  heat,  you  have  caused  the  zinc  and  the  sulphur  to 
disappear,  and  in  their  place  you  have  a  substance  which  is  distinctly 
different  from  each  of  the  original  substances.  This  is  a  change  of 
identity,  a  chemical  change  ;  and  with  this  meaning,  the  new  substance, 
which  for  the  moment  may  be  designated  x,  is  said  to  contain  zinc  and 
sulphur,  and  the  latter  are  said  to  be  combined  in  the  substance  x.  To 
the  question,  Does  the  substance  x  contain  nothing  but  zinc  and  sul- 
phur ?  the  answer  will  be  suggested  by  the  next  experiment. 


INTRODUCTION  5 

Behavior  with  iron. — Weigh  out  carefully  3.20  grams  of  13/2 
sulphur  powder ;  also  5.60  grams  of  finely  divided  iron  (iron 
dust).  Mix  them  thoroughly  in  the  mortar.  Take  out  a 
portion,  ignite  it,  and  compare  the  product  with  the  iron, 
with  the  sulphur,  and  with  the  mixture  by  inspection  and 
by  its  behavior  with  hydrogen  chloride,  as  in  the  preceding 
experiment.  Does  the  gas  which  is  obtained  have  the  same 
odor  and  action  on  paper  wet  with  lead  acetate  as  in  the 
preceding  ? 

(a)  Vary  this  procedure  as  follows :  Put  a  portion  of  the 
mixed  iron  and  sulphur  in  a  dry  test-tube,  and  cork  the  lat- 
ter ;  weigh  it  and  its  contents  carefully  to  tenths ;  then, 
holding  it  nearly  horizontal,  tap  it  gently  so  that  the  pow- 
der spreads  out  in  an  elongated  pile  from  the  bottom  of  the 
tube ;  let  the  cork  lie  loosely  in  the  mouth  of  the  test-tube, 
and  heat  the  other  end  in  the  flame  just  enough  to  start  the 
action  ;  then  remove  from  the  flame.  When  the  action  has 
ceased,  let  cool,  and  weigh  again  with  contents.  With  a  lit- 
tle care,  you  will  be  able  to  do  this  without  losing  anything 
from  the  tube  during  the  operation.  Save  the  product. 

EXPLANATORY  NOTE. — Again  you  have  a  chemical  change.  The 
substance  produced  (y)  contains  iron  and  sulphur  as  constituents,  but 
is  neither  iron  nor  sulphur ;  moreover,  it  contains  nothing  bid  these, 
since  what  you  have  in  the  tube  after  the  change  weighs  no  more  than 
the  iron  and  the  sulphur  which  you  put  in.  Iron  and  sulphur  then 
must  be  the  sole  constituents  of  the  substance  y ;  zinc  and  sulphur  are 
likewise  the  sole  constituents  of  the  substance  x.  The  first  is  therefore 
named  iron  sulphide,  and  is  said  to  be  composed  of  iron  and  sulphur,  and 
the  second  is  zinc  sulphide,  and  is  composed  of  zinc  and  sulphur.  The  " 
changes  by  which  these  are  produced  fall  under  a  common  type,  which 
may  receive  a  general  expression,  thus :  Substance  A  and  substance  B 
became  substance  A  B  (composition) ;  or,  to  express  it  more  concisely, 

A  +  B  =  A  B. 

But  you  have  further  illustration  of  chemical  change  in  the  produc- 
tion of  a  peculiar  gas  by  the  action  of  the  hydrogen  chloride  on  both 
zinc  sulphide  and  iron  sulphide.     This  gas  is  clearly  very  different  from 
all  these  other  substances.     You  have  noted  the  same  odor  and  the   ' 
18 


6  ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

same  action  on  the  lead  paper  in  both  cases,  and,  in  fact,  the  same  gas 
is  produced  by  both  substances.  If  this  is  so,  evidently  neither  iron 
nor  zinc  can  enter  into  its  composition.  But  the  sulphur  of  one  or  of 
the  other  does  so  enter,  yet  the  gas  is  markedly  different  from  sulphur 
itself  and  from  the  gas  produced  by  burning  sulphur  (see  Exp.  13). 
The  sole  other  constituent  of  this  peculiar  gas  is  hydrogen,  which  comes 
from  the  hydrogen  chloride,  of  which  also  it  is  a  constituent.  The  gas 
is  therefore  named  hydrogen  sulphide.  It  is  also  known  as  hydrosul- 
phuric  acid. 

13/3  To  show  that  hydrogen  sulphide  contains  sulphur:  Place 
about  1  gram  (not  more  than  2)  of  the  iron  sulphide,  made 
in  the  previous  experiment,  in  the  gas  generator  (see  Ap- 
pendix, 6-9)  with  just  enough  water  to  seal  the  thistle-tube. 
Drop  the  delivery  tube  into  a  test-tube  about  one  third 
filled  with  nitric  acid  (handle  this  substance  with  care,  for 
it  is  very  corrosive  *),  so  that  the  gas  shall  bubble  through 
this  liquid.  Pour  a  few  drops  of  hydrogen  chloride  into 
the  thistle-tube  of  the  generator,  so  as  to  produce  a  quick 
stream  of  bubbles  through  the  liquid.  Place  a  bit  of  paper 
wet  with  lead  acetate  over  the  mouth  of  the  test-tube.  As 
the  gas  from  the  generator  passes  through  the  nitric  acid 
you  see  small  particles  of  white  or  yellowish  substance 
appearing,  which,  when  the  action  has  ceased,  or  nearly  so, 
will  have  collected  into  a  mass  from  which  you  may  rinse 
the  acid  with  water,  and  which  you  may  easily  recognize  as 
sulphur  by  inspection  and  by  burning.  At  the  same  time 
the  lead  paper  may,  perhaps,  show  no  blackening,  since  the 
sulphur  is  produced  only  at  the  expense  of  the  hydrogen 
-  sulphide,  although  enough  of  the  latter  to  stain  the  paper 
may  escape  destruction  by  the  nitric  acid. 

EXPLANATORY  NOTE. — Hydrogen  sulphide,  therefore,  contains  sul- 
phur, and,  whenever  this  gas  is  produced,  it  may  be  taken  as  evidence 
of  sulphur  as  a  constituent  in  the  substances  from  which  it  is  produced. 

*  If  nitric  acid  is  spilled  on  the  skin,  clothing,  or  table,  the  spot 
should  be  as  quickly  as  possible  moistened  with  ammonia  (side-table), 
:    and  then  rinsed  with  water. 


INTRODUCTION  7 

QUESTIONS. — How  can  you  differentiate  (that  is,  distinguish  by  dif- 
ferences) between  sulphur,  and  oxygen,  and  sulphur  dioxide  ?  Between 
zinc,  and  sulphur,  and  the  mixture  of  zinc  and  sulphur,  and  zinc  sul- 
phide? Between  iron,  and  sulphur,  and  the  mixture  of  iron  and  sul- 
phur, and  iron  sulphide?  What  constitutes  the  difference,  by  defi- 
nition, between  a  mixture  and  a  chemical  compound  ?  (see  Nos.  13  and 
28,  Part  I.)  How  do  you  bring  about  the  chemical  change  between 
sulphur  and  air,  between  zinc  and  sulphur,  between  iron  and  sulphur? 
What  evidence  by  observation  have  you  that  heat  is  produced  by  these 
three  changes?  Does  zinc  sulphide,  made  by  heating  zinc  and  sulphur, 
change  back  to  zinc  and  sulphur  by  cooling?  Does  iron  sulphide  re- 
verse the  change  by  cooling  ?  Is  the  change  from  iron  and  sulphur 
mixed  to  iron  sulphide  accompanied  by  change  in  the  total  weight? 
(see  No.  14,  Part  I.) 

3.  Additional  Illustrations  of  Chemical  Change 

Composition. — Put  in  a  dry  test-tube  about  1  gram  of  lead  15/1 
dust  and  0.2  of  a  gram  of  iodine  (iodine  must  be  weighed 
on  glass  or  paper,  as  it  corrodes  metal) ;  cork  the  tube 
and  weigh  it  with  its  contents  carefully ;  let  the  cork  lie 
loosely  in  the  mouth  of  the  test-tube  and  warm  the  mixture 
very  slightly,  at  first  barely  touching  the  flame  with  the 
bottom  of  the  tube.  When  the  first  action  is  over,  the  sub- 
stance may  be  heated  until  it  melts.  A  little  of  the  iodine 
may  escape  the  change,  making  a  purple  vapor  and  a  dark 
deposit  on  the  upper  part  of  the  tube.  When  the  tube  is 
cool,  weigh  it  with  its  content.  Describe  the  phenomenon, 
and  compare  the  yellow  substance  with  the  lead  and  with 
the  iodine.  Preserve  a  sample  of  it  for  future  comparison. 

EXPLANATORY  NOTE. — From  lead  and  iodine  is  produced  a  substance 
which  does  not  give  off  a  purple  vapor,  nor  impart  a  brown  color  to  water, 
as  does  iodine,  and  which  is  clearly  neither  iodine  nor  lead  ;  yet  by  the 
test  of  weight  it  can  contain  nothing  more  than  iodine  and  lead.  This 
bright-yellow  substance  is  named  lead  iodide.  Does  it  dissolve  in  water? 

Composition. — Put  about  0.3  of  a  gram  of  magnesium   15/2 
ribbon,  or  powder,  in  the  porcelain  crucible   (see  Appen- 
dix,  11).     Weigh  carefully  the  crucible  with  its  content 


8  ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

and  its  lid.  Support  the  same  on  the  pipe-stem  triangle, 
and  the  latter  on  the  iron  ring  of  the  stand.  Apply  the 
full  heat  of  the  flame  to  the  bottom  of  the  crucible  for  ten 
or  fifteen  minutes.  Eaise  the  lid  slightly  to  observe  what 
is  taking  place,  but  do  not  let  any  of  the  white  smoke 
escape.  During  the  last  few  minutes  the  lid  should  be 
entirely  removed.  Let  the  crucible  cool,  and  weigh  it 
again  with  content  and  lid.  How  do  the  two  weights  com- 
pare ?  Describe  the  phenomenon  and  compare  the  sub- 
stance after  heating  with  the  original.* 

EXPLANATORY  NOTE. — The  bright  metallic  ribbon  or  powder  is 
changed,  simply  by  heating  in  contact  with  the  air,  to  a  very  different 
substance — a  grayish  chalklike  powder  ;  but  this  weighs  more  than  the 
original.  It  must  be,  therefore,  that  something  besides  magnesium  is 
contained  in  the  product.  This  "  something  "  comes  from  the  air,  is  an 
invisible  gas,  and  is  named  oxygen.  The  white  powder  is  named  mag- 
nesium oxide.  Try  also  heating  a  short  piece  of  the  ribbon  directly  in 
the  flame,  holding  it  with  the  tongs ;  likewise  a  little  of  the  oxide. 

15/3  Composition. — In  a  similar  manner  heat  in  the  crucible 
about  2  grams  of  zinc  dust,  weighing  the  crucible  and 
contents  before  and  after  the  ignition.  Compare  the 
weights  and  describe  the  phenomenon.  Zinc  oxide  is  thus 
formed — yellow  while  hot,  white  when  cold.  Try  also  heat- 
ing a  little  of  the  zinc  dust  on  the  spatula  blade.  Preserve 
a  little  of  the  zinc  oxide  for  future  comparison. 

15/4  Composition.— Spread  about  4  grams  of  lead  dust  on  the 
crucible  lid,  weighing  the  whole ;  then  ignite  over  the  flame 
for  fifteen  or  twenty  minutes  and  weigh  again.  The  red- 
dish-yellow powder  is  lead  oxide.  Preserve  a  little  of  this. 

EXPLANATORY  NOTE. — The  statement  made  concerning  magnesium 
oxide  applies  also  to  zinc  and  lead  oxides. 

These  four  instances  of  composition  are  changes  of  the  general  form: 
Substance  A  and  substance  B  become  substance  A  B ;  or 
A  +  B  =  A  B. 

*  Clean  the  crucible  by  using  a  few  drops  of  hydrochloric  acid,  warm- 
ing gently,  then  rinsing  with  water.  Scouring  with  sand  may  be  helpful. 


INTRODUCTION  9 

QUESTION. — Have  you  evidence  that,  when  magnesium  changes  to 
magnesium  oxide,  and  zinc  to  zinc  oxide,  heat  is  produced  f 

Decomposition. — Take  a  quantity  of  lead  nitrate,  about  16/1 
1  gram  (twice  the  size  of  a  pea),  pulverize  finely  in  a 
clean,  dry  mortar,  shake  the  powder  into  a  clean,  dry  test- 
tube,  wipe  off  any  particles  adhering  to  the  upper  part  of 
the  tube,  cork,  and  weigh  the  tube  and  contents.  Then, 
holding  the  tube  nearly  horizontal  (paper  holder),  with  the 
cork  loosely  placed  in  its  mouth,  warm  the  substance  gently 
until  the  snapping  (decrepitation)  ceases  and  the  powder 
melts  quietly ;  remove  the  cork  and  continue  the  heating 
until  the  bubbling  ceases  and  the  glass  begins  to  soften. 
Note  the  effect  of  the  brown  gas  on  wet,  blue  litmus  paper. 
Let  cool,  and  weigh  the  tube  and  contents,  including  the 
cork.  Break  the  tube  and  examine  the  reddish-yellow  resi- 
due, lead  oxide.  Save  a  little  of  this  for  future  reference. 

QUESTIONS. — Does  the  residue  dissolve  in  water?  Does  the  lead 
nitrate  dissolve  in  water  ?  Does  the  brown  gas  condense  at  all  on  the 
upper  part  of  the  test-tube  as  you  saw  in  the  heating  of  sulphur  f  (see 
Exp.  11.)  How  does  the  weight  of  the  residue  compare  with  that  of 
the  lead  nitrate  ? 

EXPLANATORY  NOTE. — In  this  experiment  you  see  one  substance 
yielding  at  least  two  others,  distinctly  differing  from  each  other  as  well 
as  from  the  original ;  and  at  least  one  of  these — that  is,  the  residue  in 
the  tube — weighs  less  than  the  original,  which  has  disappeared,  although 
none  of  the  latter,  unchanged,  has  passed  out  of  the  tube.  The  gas 
which  has  passed  out,  named  nitrogen  tetroxide,  and  the  residue,  named 
lead  oxide  (see  Exp.  15/4),  which  is  left  in  the  tube,  must  have  been 
contained  in  the  lead  nitrate  which  has  been  destroyed ;  the  latter  has 
been  broken  up  into  at  least  two  other  substances,  each  of  which  weighs 
less  than  the  original.  Such  a  change  is  called  decomposition.  It  may 
be  described  under  the  general  type :  Substance  A  B  becomes  sub- 
stance A  and  substance  B ;  or 

A  B  =  A  +  B. 

Decomposition. — Place  about  1  gram  of  zinc  nitrate  in  a  16/2 
test-tube,  weigh  the  tube  and  contents,  then  heat.   Describe 
the  phenomenon,  and  note  the  clear  liquid  which  condenses 


10          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

on  the  upper  part  of  the  tube.  This  is  water  ;  it  is  slowly 
driven  from  the  tube  by  heat.  Later,  note  the  brown  gas, 
which  appears  as  in  the  preceding  experiment.  This  is 
nitrogen  tetroxide,  and  it  in  turn  is  driven  from  the  tube. 
Finally,  there  is  left  a  powder  which  no  longer  melts,  and 
which  is  yellow  while  hot  and  white  when  cold.  This  is 
zinc  oxide.  Weigh  again  the  tube  and  contents.  Examine 
the  residue  left  in  the  tube  (comparing  with  the  substance 
in  Exp.  15/3),  and  save  a  portion  for  future  tests. 

QUESTIONS.  —  Does  the  residue  weigh  more  or  less  than  the  zinc 
nitrate  from  which  it  comes  f  Does  it  dissolve  in  water  ?  Does  zinc 
nitrate  dissolve  in  water  ? 

EXPLANATORY  NOTE.  —  You  see  the  substance,  zinc  nitrate,  destroyed 
by  heat,  yielding  at  least  three  distinctly  different  substances  —  water, 
nitrogen  tetroxide,  and  zinc  oxide  ;  and  the  last  of  these,  and  by  infer- 
ence each  of  the  others  also,  weighs  less  than  the  original  substance, 
and  all  of  them  must  have  been  contained  in  the  original  zinc  nitrate. 
This  change  falls  under  the  same  type  as  the  preceding  : 


17/1  Substitution.  —  (a)  Place  a  small  quantity  of  granulated 
zinc,  about  0.5  of  a  gram,  in  a  test-tube  ;  add  to  it  a  few 
drops  of  hydrochloric  acid  (hydrogen  chloride).  Note  the 
effervescence  which  implies  the  liberation  of  a  gas.  Close 
the  tube  with  the  thumb  for  a  few  seconds,  then  open  it, 
holding  its  mouth  to  the  gas  flame.  Note  what  takes  place. 

EXPLANATORY  NOTE.—  The  colorless  invisible  gas  liberated  in  this 
change  burns  with  an  almost  invisible  flame,  and  makes  with  air  an 
explosive  mixture.  This  causes  the  slight  sound  when  the  content  of 
the  tube  is  ignited.  Larger  quantities  may  be  dangerously  explosive, 
and  this  fact  should  always  be  in  mind  when  dealing  with  this  gas 
which  is  named  hydrogen. 

(b)  Next,  place  1  gram  of  granulated  zinc  in  a  small 
evaporating  dish  which,  with  a  small  glass  stirring-rod  (see 
Appendix,  12),  has  been  previously  weighed  (to  tenths  is 
sufficient).  Add  about  one  quarter  of  a  test-tubeful  of 
hydrochloric  acid,  in  portions  at  a  time,  warming  some- 


INTRODUCTION  11 

what  the  contents  of  the  dish.  Holding  a  lighted  match 
at  the  surface  of  the  liquid  while  the  bubbles  of  hydrogen 
are  breaking,  will  again  show  the  combustibility  of  this  gas. 
When  the  zinc  has  disappeared  except  a  few  black  specks, 
and  the  bubbles  of  gas  no  longer  appear,  increase  the  heat 
somewhat,  holding  the  burner  in  the  hand  and  touching 
the  tip  of  the  small  flame  to  the  bottom  of  the  dish  from 
time  to  time,  as  may  be  needed  to  keep  the  liquid  quietly 
boiling  (see  Appendix,  12).  This  soon  thickens  and  de- 
posits at  the  edges.  Continue  the  heating,  avoid  spatter- 
ing as  much  as  possible,  and  soon  white  fumes  appear,  and 
the  substance  solidifies  if  cooled.  At  this  point  cease  the 
heating  and,  when  the  dish  is  cool,  weigh  it  with  its  con- 
tents. Describe  the  substance  in  the  dish.  Does  it  weigh 
more  or  less  than  the  zinc  taken  ?  Let  some  of  it  remain 
exposed  to  the  atmosphere  for  a  short  time  and  note  the 
change. 

EXPLANATORY  NOTE. — Hydrochloric  acid  contains  as  sole  constit- 
uents hydrogen  and  chlorine,  the  material  which  you  use  being  this 
substance  dissolved  in  water.  When  this  is  brought  in  contact  with 
zinc  a  change  takes  place,  and,  when  this  is  complete  and  the  liquid 
boiled  to  dryness,  the  product  just  seen  is  the  result.  Now  this  weighs 
more  than  the  zinc,  nearly  double,  and,  therefore,  must  contain  some- 
thing besides  zinc ;  yet  it  can  not  contain  anything  more  than  zinc, 
hydrochloric  acid,  and  water ;  indeed,  it  can  not  contain  all  of  these, 
for  hydrogen  has  passed  into  the  air,  as  you  have  seen,  and  the  water 
also  has  been  boiled  away.  In  fact,  the  residue  in  the  dish  is  a  sub- 
stance which  contains  as  sole  constituents  the  zinc  used  and  the 
chlorine  previously  contained  in  the  acid,  although  it  is  very  different 
from  each  of  these.  It  is  named  zinc  chloride.  Exposure  of  this  to 
the  air  for  a  short  time  will  show  you  incidentally  one  of  its  proper- 
ties; it  absorbs  water  from  the  atmosphere  and  liquefies  in  conse- 
quence (deliquescence).  In  this  change  it  is  seen  that  a  constituent  of 
hydrochloric  acid — namely,  hydrogen — leaves  the  substance,  and  zinc 
may  be  said  to  take  its  place  ;  so  that,  starting  with  zinc  and  hydrogen 
chloride,  you  obtain  hydrogen  and  zinc  chloride.  Such  a  change  is 
called  substitution.  It  may  be  represented  by  the  general  form  : 


12          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

17/2  Substitution. — Optional  experiment. — (a)  Place  about  0.5 
of  a  gram  of  granulated  zinc  in  a  test-tube,  add  dilute  sul- 
phuric acid,  warm,  and  test  the  gas  at  the  flame  as  in  the 
preceding  experiment. 

(b)  Next  place  about  3  grams  of  granulated  zinc  in  the 
evaporating  dish,  add  about  one  t'est-tubeful  of  dilute  sul- 
phuric acid  (one  volume  of  concentrated  acid  to  four  of 
water)  and  an  equal  volume  of  water,  and  warm.  When 
the  zinc  has  disappeared,  or  nearly  so,  filter  (see  Appendix, 
13),  boil  down  the  liquid  somewhat,  and  set  aside  to  crys- 
tallize. Crystals  of  zinc  sulphate  are  thus  obtained.  The 
relation  of  this  substance  to  sulphuric  acid  is  similar  to  that 
of  zinc  chloride  to  hydrochloric  acid.* 

17/3  Substitution. — Place  about  3  grams  of  lead  powder  in  a 
small  evaporating  dish,  add  about  one  quarter  test-tubeful 
of  nitric  acid  and  an  equal  volume  of  water.  Heat  gently 
until  the  action  ceases,  filter  the  liquid,  and  set  it  aside  to 
crystallize.  When  there  is  a  considerable  deposit  of  crys- 
tals, drain  off  the  liquid,  and  throw  the  crystals  on  two  or 
three  thicknesses  of  filter  paper  to  absorb  the  adhering 
liquid.  These  are  crystals  of  lead  nitrate.  Heat  a  por- 
tion of  these  and  compare  the  result  with  that  in  Kos. 
15/4,  and  16/j.  Save  a  portion  of  the  crystals,  labeled, 
for  later  use. 

.17/4  Substitution. — Optional  experiment. — Dissolve  about  10 
grams  of  crystallized  copper  sulphate  in  about  50  cubic 
centimeters  (see  Appendix,  14)  of  boiling  water,  using  the 
larger  evaporating  dish.  Add  to  this  4  grams  of  granu- 
lated zinc,  and  boil  the  liquid  gently  until  the  blue  color 
has  entirely  disappeared.  Filter;  concentrate  the  liquid 
to  about  one  third  its  volume ;  filter  again  if  necessary,  and 
set  aside  to  crystallize.  What  is  the  reddish-brown  powder 

*  The  irritation  which  may  be  caused  by  the  fumes  and  spray  in 
this  experiment,  if  many  are  working  it  at  the  same  time,  may  be  re- 
lieved by  inhaling  moderately  the  fumes  from  the  bottle  of  ammonium 
hydroxide  (side-table). 


OF  THE 

INTRODUCTION  UN1VEH      13 


which  appears  when  the  zinc  is  added  ?  Adt&ps 
of  nitric  acid  to  this  powder  after  filtration.  What  is  the 
substance  which  crystallizes  in  the  filtrate  ? 

EXPLANATORY  NOTE.  —  Copper  sulphate  bears  the  same  relation  to 
copper  and  sulphuric  acid  that  zinc  sulphate  bears  to  zinc  and  sul- 
phuric acid  (see  Exp.  17/2)  —  that  is,  copper  has  taken  the  place  of  hy- 
drogen as  a  constituent  in  sulphuric  acid.  When  zinc  is  brought  in 
contact  with  the  solution  of  copper  sulphate,  the  copper,  in  turn,  is  dis- 
placed, appearing  as  a  powder,  which,  with  nitric  acid,  reproduces  a  blue 
solution  ;  while  the  zinc,  with  the  sulphuric  acid,  forms  zinc  sulphate, 
crystallizing  as  seen  in  Exp.  17/2  .  Iron  may  likewise  thus  substitute 
itself  for  copper  as  constituent.  If  the  action  is  allowed  to  take  place 
slowly  in  dilute  solution,  the  copper  may  be  deposited  as  a  film  on  an 
object  of  iron,  such  as  a  knife-blade.  This  is  cajled  "  plating." 

Double  exchange.  —  The  purpose  of  this  experiment  is  to   18 
illustrate  a  reaction  of  the  type  : 


This  is  known  as  double  exchange  or  double  decomposition  ; 
it  is  also  described  as  a  metathetic  reaction.  The  experi- 
ment is  rather  long,  so  its  plan  is  here  given  as  a  whole  : 

A.  To  prepare  zinc  iodide  from  zinc  and  iodine  : 

(a)  To  show  that  this  is  neither  zinc  nor  iodine. 

(b)  To  show  that  it  contains  both  zinc  and  iodine. 

(c)  To  prepare  the  solution  of  zinc  iodide  in  water. 

B.  To  prepare  lime  sulphide  in  solution  by  water  from 

lime  and  sulphur. 

.(d)  To  show  that  this  contains   sulphur  as  con- 
stituent. 

C.  To  mix  the  solution  of  zinc  iodide  and  that  of  lime 

sulphide,  a  chemical  change  taking  place 
by  which  a  liquid  and  an  insoluble  solid  are 
produced. 

(e)  To  show  that  the  liquid  now  contains  lime  and 
iodine  in  combination,  but  no  zinc  nor  sul- 
phur. 


14          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

(/)  To  show  that  the  insoluble  solid  contains  zinc 
and  sulphur  in  combination,  but  no  iodine 
nor  lime. 

Conclusion. — Zinc  iodide  and  lime  sulphide  have  become 
zinc  sulphide  and  lime  (calcium)  iodide. 

18/A  A.  To  prepare  zinc  iodide. — AVeigh  a  clean,  small  evapo- 
rating dish  and  a  short  glass  rod  to  tenths  of  a  gram.  Place 
in  the  dish  1  gram  of  granulated  zinc  and  a  few  drops  of 
water. 

Weigh  out  3.9  grams  of  iodine  (on  glass  or  on  paper). 
Add  about  one  fourth  or  one  fifth  of  the  iodine  to  the  zinc 
in  the  dish,  stir,  and  warm  very  slightly,  just  enough  to 
start  the  change  which  itself  produces  much  heat.  When 
the  action  seems  to  cease,  add  again  about  the  same  quan- 
tity of  iodine,  stirring  constantly,  and  so  on  until  all  has 
been  used.  This  gives  a  small  volume  of  dark-colored 
liquid.  Holding  the  burner  in  the  hand  (see  Appendix, 
12),  heat  from  time  to  time  to  keep  the  liquid  gently  boil- 
ing. There  is  some  escape  of  purple  fumes  for  a  few  sec- 
onds ;  this  vapor  is  irritating,  so  avoid  inhaling  it.  When 
the  contents  thicken  there  is  a  tendency  to  spatter ;  pre- 
vent this  by  constant  stirring  and  moderating  the  heat. 
Finally,  when  the  contents  seem  thoroughly  dry,  white 
fumes  begin  to  escape.  At  this  point  cease  heating.  The 
product  is  a  dry  powder  slightly  brownish  in  color.  When 
the  dish  is  cool,  weigh  it  with  its  contents.  The  substance 
weighs  more  than  the  zinc,  but  somewhat  less  than  the 
zinc  and  iodine  together,  owing  to  loss  by  the  heating.* 

(a)  To  show  that  this  is  neither  zinc  nor  iodine:  You 
have  seen  that  it  shows  no  purple  fumes  upon  heating,  as 
iodine  would  show. 

Place  a  small  portion,  such  as  would  be  taken  on  the 
point  of  a  penknife,  in  a  test-tube  with  a  few  drops  of 


*  Iodine  stains  may  generally  ba.  removed  by  using  sodium  sulphite 
or  ammonium  sulphide. 


INTRODUCTION  15 

water.     It  dissolves  as  zinc  would  not,  but  with  no  brown 
color  such  as  iodine  would  impart. 

(b)  To  show  that  it  contains  both  zinc  and  iodine :  Place 
another  small  portion  in  a  small  evaporating  dish,  add  to  it 
a  drop  of  nitric  acid,  and  heat  to  complete  dryness.     You 
see  the  purple  vapor  of  iodine,  and  have  left  in  the  dish ' 
zinc  oxide,  as  seen  in  Exps.  15/3  and  16/2. 

(c)  Dissolve  the  rest  of  the  product,  zinc  iodide,  in  50 
cubic  centimeters  of  water  (see  Appendix,  14).     You  may 
see  some  of  the  original  zinc  unacted  upon.     Filter  the 
solution  (see  Appendix,  13).    Turn  a  few  drops  of  the  filtrate 
(that  is,  the  liquid  which  has  passed  through  the  filter) 
into  a  test-tube,  and  add  a  few  particles  of  lead  nitrate 
(see  Exp.  17/3)  previously  dissolved  in  water.     The  bright- 
yellow  powder  now  appearing  in  the  liquid  is  lead  iodide, 
seen  also  in  Exp.  15/j,  and  must  be  taken  as  further  evi- 
dence of  iodine  as  a  constituent  in  the  substance  formed  in 
18/A.     Set  aside  the  remainder  of  the  solution  and  label  it 
zinc  iodide.     To  what  type  of  change  does  this  formation  of 
zinc  iodide  belong  ? 

B.  To  prepare  calcium  or  lime  sulphide  in  solution. —  18/B 
Place  5  grams,  roughly  weighed,  of  powdered  lime  in 
the  larger  evaporating  dish.  Add  100  cubic  centimeters 
of  water  and  boil.  Touch  a  piece  of  red  litmus  paper 
to  the  liquid  and  note  the  effect.  Add  to  the  contents 
of  the  dish  3.2  grams,  roughly  weighed,  of  sulphur  pow- 
der (flowers)  and  boil,  stirring  constantly.  Keep  the  liquid 
boiling  gently  for  a  few  minutes,  until  it  becomes  colored 
quite  a  deep  yellow.  Cease  the  heating,  and  the  powder 
quickly  settles  to  the  bottom.  Drain  off  the  liquid  as 
much  as  practicable  without  disturbing  the  sediment  (this 
is  called  decanting),  pouring  the  former  upon  a  filter.  Add 
again  100  cubic  centimeters  of  water  to  the  contents  of 
the  dish,  boil  until  well  colored,  let  it  settle,  and  decant 
upon  the  filter.  Do  this  four  times,  which  will  give  300 
cubic  centimeters  or  more  of  clear  liquid.  This  will  prob- 


16          ELEMENTARY  PRINCIPLES  OP  CHEMISTRY 

ably  be  enough,  but  if  more  is  needed,  it  is  only  neces- 
sary to  add  another  portion  of  water  and  repeat  the  oper- 
ation. Try  the  action  of  this  yellow  liquid  on  the  red 
litmus  paper. 

(d)  To  show  that  sulphur  is  a  constituent  of  this  liquid : 
'Take  about  one  half  test-tubeful,  add  hydrochloric  acid,  and 

heat,  holding  at  the  mouth  of  the  tube  a  piece  of  filter 
paper,  wet  with  lead  acetate  solution.  What  is  the  effect  ? 
You  also  see,  reappearing  in  the  liquid,  yellow,  or  nearly 
white,  very  finely  divided  sulphur. 

The  yellow  liquid  obtained  in  18/B  may,  for  present 
purposes,  be  considered  as  a  solution  in  water  of  lime  sul- 
phide or  calcium  sulphide,  a  substance  containing  lime  and 
sulphur  in  combination. 

18/C  0.  The  reaction,  double  exchange,  between  zinc  iodide  and 
lime  sulphide. — Pour  about  one  half  the  solution  of  zinc 
iodide,  prepared  in  (c),  into  one  of  the  larger  beakers  and 
drop  in  a  piece  of  red  litmus  paper.  Now,  both  solutions 
being  hot,  pour  the  lime  sulphide  slowly  into  the  zinc  iodide, 
a  little  at  a  time,  constantly  stirring,  until  the  paper  first 
turns  permanently  blue.  Be  careful  to  avoid  any  unneces- 
sary addition  of  lime  sulphide  beyond  this  point.  You  see 
a  white  insoluble  solid,  a  powder,  form  in  the  midst  of  the 
liquid,  and  settle  to  the  bottom.  A  substance  formed  in 
this  manner  is  called  a  precipitate,  and  the  operation  is  pre- 
cipitation. 

(e)  To  show  that  the  liquid  notv  contains  lime  and  iodine 
in  combination,  but  no  zinc  nor  sulphur :  Let  the  precipitate 
obtained  in  0  settle  well  to  the  bottom  of  the  beaker ;  then, 
without  disturbing  it,  pour  off  as  much  of  the  liquid  as  pos- 
sible upon  a  filter.     Fill  up  the  beaker  with  warm  water, 
stir  the  precipitate,  let  settle,  and  again  decant  the  liquid 
upon  the  filter,  collecting  what  runs  through  with  the  first 
portion.    Label  this,  filtrate  (e),  and  set  it  aside.    Again  fill 
the  beaker  with  water,  stir  the  precipitate,  and  set  this  aside 
to  settle,  labeling  it,  precipitate  (e). 


INTRODUCTION  1? 

From  filtrate  (e)  take  about  one  half  test-tubef ul,  and  add 
to  this  a  few  drops  of  lime  sulphide  solution.  The  absence 
of  precipitation  may  be  taken  as  evidence  of  the  absence  of 
zinc,  or  perhaps,  more  strictly  speaking,  of  zinc  iodide. 

Take  again  one  half  test-tubeful  of  filtrate  (e),  and  add  a 
'few  drops  of  lead  nitrate  solution.  The  bright-yellow  pre- 
cipitate is  recognized  as  lead  iodide,  and  shows  the  pres- 
ence of  iodine  in  combination. 

Boil  the  rest  of  filtrate  (e)  to  dryness  in  the  smaller  evap- 
orating dish,  having  care  to  moderate  the  heat  as  the  liquid 
thickens,  so  as  to  avoid  spattering  and  possibly  cracking 
the  dish.  When  the  last  of  the  liquid  disappears,  the  full 
heat  of  the  flame  may  be  applied.  As  a  result,  you  see  the 
purple  vapor  of  iodine  appear.  Continue  the  heating  as 
long  as  iodine  is  liberated,  and  you  have  left  finally  in  the 
dish  a  white,  chalklike  powder. 

That  this  residue  is  not  zinc  oxide,  you  may  see  by  its 
color  and  by  adding  to  the  whole,  or  a  portion  of  it,  a  very 
small  quantity  of  water,  boiling  and  testing  the  liquid 
with  red  litmus  paper. 

That  this  residue  does  not  contain  sulphur,  you  may 
see  by  adding  hydrochloric  acid,  boiling,  and  testing  the 
vapor  by  paper  wet  with  lead  acetate  solution.  In  fact,  it 
is  lime,  the  substance  with  which  you  started. 

(/)  To  show  that  the  ivhite  precipitate  (e)  contains  zinc  and 
sulphur,  lut  no  iodine  nor  lime  :  Pour  the  liquid  and  the 
precipitate  which  was  labeled  precipitate  (e)  upon  the  filter. 
When  the  liquid  has  filtered  through,  fill  the  funnel  with 
water,  not  quite  up  to  the  edge  of  the  paper,  and  when  this 
has  passed  through  fill  it  a  second  time.  The  precipitate 
is  thus  washed  free  of  soluble  matter.  Take  out  a  portion 
of  the  wet  precipitate  and  dry  it  by  the  heat  of  the  flame, 
holding  it  on  the  spatula  blade  or  the  asbestos. 

Drop  some  of  the  dried  substance  into  a  test-tube,  add 
hydrochloric  acid,  boil,  and  test  the  vapor  as  before  for 
hydrogen  sulphide. 


18          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

Drop  another  portion  of  the  dried  substance  into  a 
small  evaporating  dish,  barely  moisten  it  with  nitric  acid. 
evaporate  the  acid  by  gentle  heat,  then  heat  with  the  full 
flame.  You  see  sulphur  appear  and  burn,  but  no  iodine, 
and  you  have  left  finally  zinc  oxide,  seen  also  in  Exps.  15/3 
and  16/2  .  Boil  another  portion  of  the  dried  substance  with 
a  little  water,  and  test  by  red  litmus  to  see  that  it  is  not 
lime. 

EXPLANATORY  NOTE.  —  By  the  operation  in  18/A  you  have  combined 
zinc  and  iodine,  making  zinc  iodide  ;  in  18/B  you  have  combined  lime 
and  sulphur,  forming  lime  or  calcium  sulphide  ;  by  mixing  the  solu- 
tions of  these  two  substances  you  have  obtained  an  insoluble  solid 
which  contains  zinc  and  sulphur  combined  —  that  is,  zinc  sulphide  —  and 
at  the  same  time  you  have  a  liquid  which  contains  lime  and  iodine  com- 
bined —  that  is,  lime  or  calcium  iodide.  Thus  the  two  substances,  zinc- 
iodide  and  lime  sulphide,  with  which  you  started,  have  exchanged  con- 
stituents and  produced  two  entirely  different  substances.  Such  a  change 
is  expressed  by  the  general  form  : 


As  to  Notation. 

19  There  is  used  in  chemistry,  for  the  purpose  of  designating  substances 
and  describing  changes,  a  system  of  symbols,  which,  at  this  early  stage 
of  the  study,  may  best  be  regarded  as  a  system  simply  of  arbitrary 
signs,  although  it  really  has  a  much  deeper  significance.  Thus  the  fol- 
lowing symbols  are  used  :  For  sulphur,  S  ;  for  oxygen,  0  ;  for  zinc,  Zn  ; 
for  iron,  Fe  (Latin,  ferrum);  for  hydrogen,  H  ;  for  sulphur  dioxide, 
S0a,  signifying  qualitatively  that  it  is  made  of  sulphur  and  oxygen,  or 
contains  these  as  sole  constituents  ;  for  zinc  sulphide,  ZnS,  and  for  iron 
sulphide,  FeS,  since  they  contain  solely  zinc  and  iron  respectively,  and 
sulphur;  for  hydrochloric  acid,  HC1,  containing  hydrogen  and  chlorine; 
for  hydrogen  sulphide  or  hydrosulphuric  acid,  H2S,  since  it  contains 
hydrogen  and  sulphur.  The  fact  that  sulphur  and  oxygen  produce  by 
chemical  change  sulphur  dioxide  is  expressed  in  equation  form  thus  : 

S  +  02  =  S02. 
The  reactions  between  sulphur  and  zinc  and  iron  are  thus  expressed  : 

Zn  +  S  =  ZnS. 

Fe  +  S  =  FeS. 


INTRODUCTION  19 

The  substance  used  under  the  label,  hydrochloric  acid,  is  really  a  19/1 
solution  of  this  substance,  HC1,  in  water.  Now,  when  hydrochloric 
acid  acts  on  zinc  sulphide,  the  hydrogen  of  the  acid  combines  with  the 
sulphur  of  the  sulphide  forming  hydrogen  sulphide,  and  the  chlorine  of 
the  acid  with  the  zinc  of  the  sulphide  forming  zinc  chloride,  ZnCl2  ; 
similarly  in  the  case  of  the  iron  sulphide.  These  reactions  are  ex- 
pressed by  the  equations  : 


FeS  +  2HC1  =  HaS  +  FeCl2. 

The  zinc  chloride,  ZnCl2,  and  the  iron  chloride,  FeCl2,  remain  dissolved 
in  the  water.  The  numerals  which  you  see  used  in  this  system  of  chem- 
ical "shorthand"  may  for  the  present  best  be  regarded  as  arbitrary 
parts  of  the  system.  In  the  "  additional  illustrations  of  chemical 
change  "  (see  Exp.  15/i  ,  etc.)  you  have  used  lead,  symbol  Pb  (Latin, 
plumbum),  and  iodine,  symbol  I,  and  lead  iodide,  symbol  PbI2  ;  mag- 
nesium, symbol  Mg  ;  zinc,  Zn,  and  oxygen,  0  ;  also  the  oxides  of  mag- 
nesium, zinc,  and  lead,  symbols  MgO,  ZnO,  and  PbO. 
What  is  the  meaning  of  the  following  equations  ? 

Pb  +  I2  =  PbI2. 
Mg  +  0  =  MgO. 
Zn  +  0  =  ZnO. 
Pb'  +  0  =  PbO. 

Referring  to  the  experiments  under  substitution  (see  Exp.  17/t  ,    19/2 
etc.),  you  should  realize  the  meaning  of  this  equation,  disregarding 
the  numerals  : 

Zn  +  2HC1  =  ZnCl2  +  H2. 

The  symbol  for  sulphuric  acid  is  H2[S04]  ;  that  is  to  say,  this  substance 
contains  hydrogen  and  something  else,  the  nature  of  which  need  not 
now  be  considered  ;  this  "  something  "  is  represented  by  the  symbol  in 
the  brackets.  The  symbol  for  zinc  sulphate  is  Zn[S04],  hence  the  reac- 
tion between  zinc  and  sulphuric  acid  is  represented  thus  : 

Zn  +  H2[S04]  =  Zn[S04]  +  H2. 

The  symbol  for  nitric  acid  is  H[N03],  and  of  lead  nitrate  is  Pb[NOs]2  ; 
hence  the  reaction  between  lead  and  nitric  acid  is  represented  thus  : 

Pb  +  2H[N08]  =  Pb[N08]a  +  H2. 
Note  that  these  last  three  equations  fall  under  the  general  form 


20          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

4.  Additional  Illustrations  of  Physical  Properties 

20  Distillation.— See  Exp.  24/6,  and  Appendix,  18,  and  Part 
I,  tfo.  12. 

20/1  Sublimation. — Heat  gently  a  small  fragment  of  iodine 
in  a  dry  test-tube.  Describe  the  phenomenon.  Kote  the 
color  of  the  vapor  and  its  odor  (cautiously),  and  its  weight 
compared  with  that  of  air  (invert  the  tube).  Does  the 
solid  melt  ?  Does  the  vapor  pass  through  the  liquid  to  the 
solid  form  on  cooling  ?  Is  the  solid  which  is  deposited  (the 
sublimate)  crystalline  or  not  ?  (See  Part  I,  Xo.  12.) 

21  Solution  and  crystallization.— Add  a  few  drops  of  hydro- 
chloric acid  to  a  few  drops  of  a  solution  of  lead  acetate  in 
a  test-tube.     What  takes  place  ?     (Precipitation.)    Boil  the 
contents  of  the  test-tube,  adding  a  little  water,  if  necessary, 
to  dissolve  the  white  powder  first  formed ;  set  aside  to  cool. 
What  takes  place  on  cooling  ? 

EXPLANATORY  NOTE. — The  white  powder  formed  on  mixing  the  two 
liquids  is  lead  chloride  (symbol,  PbCl2).  Does  its  formation  involve  a 
physical  change  or  a  chemical  change  1  It  is  not  soluble,  or  only  slightly 
so,  in  cold  water ;  hence  it  appears  as  a  solid,  a  powder,  in  the  midst  of 
the  liquid.  Lead  chloride  dissolves  in  hot  water,  and,  as  the  solution 
cools,  reappears  in  crystalline  form  ;  this  is  a  purely  physical  change. 

21/4  Solution  and  crystallization.— Dissolve  about  10  grams 
of  alum  (a  porcelain  evaporating  dish  is  convenient)  in  50 
cubic  centimeters  of  hot  water.  Filter  the  solution.  Dis- 
solve about  twice  as  much  copper  sulphate  in  a  similar 
manner.  Filter  this.  Mix  the  two  solutions;  boil  down 
to  about  one  half  the  volume,  and  set  aside  to  crystallize 
(it  may  be  left  until  the  next  day).  Can  you  distinguish 
the  two  substances  in  the  crystals?  Can  you  distinguish 
them  in  the  solution  ? 

21/7  Water  of  crystallization. — Put  about  1  gram  of  copper 
sulphate  crystals  in  a  dry  test-tube,  and  weigh  carefully 
the  tube  and  contents  ;  to  tenths  is  sufficient.  Heat  slowly, 
holding  the  tube  so  that  the  open  end  is  a  little  the  lower. 


INTRODUCTION  21 

What  condenses  on  the  cooler  portion  of  the  tube  ?  When 
the  liquid  has  disappeared  let  the  tube  cool,  and  weigh 
again.  Shake  out  the  white  dehydrated  substance,  and  let 
a  drop  of  water  from  the  finger  come  in  contact  with  a 
portion  of  it.  Observe  carefully  what  takes  place.  Bring 
a  drop  or  two  of  alcohol  in  contact  with  another  portion. 
The  dehydrated,  amorphous  substance  may  be  redissolved 
with  hot  water,  and  crystallized  as  it  was  at  first.  (See  Part 
I,  No.  21/e. ) 

Heat  in  similar  manner  some  alum  crystals,  also  some 
crystals  of  potassium  dichromate,  or  of  potassium  nitrate. 

Efflorescence   and   deliquescence. — Expose  to  the  air  for  21/8 
twenty-four  hours,  more  or  less,  (a)  some  crystals  of  sodium 
carbonate  or  of  sodium  phosphate ;  (b)  some  calcium  chlo- 
ride or  sodium  hydroxide  (see  also  Exp.  17/i  b). 

Heat  of  solution. — Determine  the  effect  on  temperature  22 
(see  Appendix,  15)  of  dissolving  in  water  (a)  some  com- 
mon salt — that  is,  sodium  chloride  (use  a  beaker  half  filled 
with  water  and  about  a  tablespoonful  of  salt) ;  (b)  some 
sodium  hydroxide ;  (c)  some  hydrochloric  acid  (concen- 
trated). 

Melting  point,  determination  of  (see  Appendix,  16). — De-  23 
termine  the  melting  point  and  freezing  point  of  paraffin 
thus  :  Prepare  a  tube  of  thin  wall  and  small  bore  by  heat- 
ing in  the  flame  a  piece  of  glass  tubing,  an  inch  or  two  from 
its  open  end,  until  the  glass  is  well  softened ;  then,  draw- 
ing it  out  slowly  until  the  bore  becomes  quite  small,  and 
finally  applying  the  flame  at  the  narrow  part  and  separat- 
ing completely  the  two  portions  of  the  tube.  The  narrow 
end  is  thus  closed  by  fusion.  Put  into  this  a  few  bits  of 
paraffin ;  warm  just  enough  to  melt  the  latter-;  shake  or  jar 
the  tube  so  that  the  liquid  shall  completely  fill  the  narrow 
portion,  leaving  no  air  bubble.  With  a  rubber  band  attach 
the  tube  alongside  the  thermometer  so  that  the  paraffin  is 
about  opposite  the  bulb.  Suspend  the  thermometer  and  * 

tube  over  a  beaker  of  water  which  is  supported  on  an  asbes- 
19 


22          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

tos  board  or  a  wire  gauze,  so  that  the  bulb  and  paraffin 
shall  be  well  immersed.  Slowly  heat  the  water  and  observe 
the  temperature  when  liquefaction  is  first  noted.  When 
this  is  complete,  let  cool,  and  observe  the  temperature  when 
solidification  begins.  Repeat  four  or  five  times,  until  the 
several  readings  of  each  point  are  fairly  concordant.  As 
the  melting  or  the  freezing  point  is  approached  the  tem- 
perature should  be  allowed  to  change  very  slowly,  and  the 
water  should  be  well  stirred.  The  freezing  point  may  be 
somewhat  lower  than  the  melting  point,  due  to  surfusion. 
24  Boiling  point,  determination  of,  and  conditions  affecting. — 
Determine  the  boiling  point  of  water  thus  (see  Appen- 
dix, 17)  :  Use  a  distilling  flask  of  about  200  or  225  cubic 
centimeters  capacity,  with  a  side  delivery  tube  carrying  a 
short  piece  of  rubber  hose.  Half  fill  with  water.  Through 
the  stopper  insert  a  thermometer  (wetting  it  first)  so  that 
the  bulb  is  below  the  exit  and  above  the  surface  of  the 
water,  high  enough  to  avoid  being  spattered  during  boil- 
ing. Support  the  whole  on  asbestos,  or  gauze,  and  the 
iron  stand  so  that  there  may  be  no  danger  of  overturning. 
Heat  until  the  liquid  boils  and  the  temperature  reaches  its 
maximum,  which  is  steadily  maintained  for  five  minutes  or 
more.  This  is  the  'boiling  point.  It  should  be,  with  a  good 
thermometer,  100°  C. ;  but  thermometers  are  often  inac- 
curate, and  may  be  corrected  by  actual  observation,  made 
with  due  care. 

Vary  the  experiment  as  follows  : 

24/1  1.  By  pinching  with  the  tongs,  close  the  rubber  exit 
tube  while  the  liquid  is  still  boiling,  and  note  the  effect  on 
temperature.  Let  it  rise  only  about  2°,  then  open  and  ob- 
serve what  takes  place. 

24/2         2.  Lower  the  thermometer  until  the  bulb  is  immersed, 

boil,  and  note  again  the  maximum  temperature,  first  with 

the  tube  open,  then  with  it  closed.     The  temperature  of 

•    the  boiling  liquid  is  likely  to  be  higher  than  that  of  the 

vapor  under  similar  conditions. 


INTRODUCTION  23 

3.  Let  it  cool  sufficiently,  then  add  to  the  water  about  24/3 
a  tablespoonful  of  salt  and  a  few  crystals  of  copper  sulphate, 
boil,  and  observe  the  temperature  of  the  vapor  as  before  (it 
should  be  unchanged). 

4.  Lower  the  thermometer  and  take  the  temperature  of  24/4 
the  boiling  solution. 

Collect  some  of  the  liquid  (distillate)  which  drops  from  24/5 
the  exit  tube.     Does  it  show  any  color  ?     Has  it  the  taste 
of  salt?     (Distillation.) 

Fit  a  test-tube  well  with  a  cork,  fill  about  one  third  with  24/1 
water,  and  boil.  After  it  has  boiled  a  few  seconds  and 
while  it  is  still  boiling,  remove  from  the  flame,  quickly  in- 
sert the  cork,  invert  the  tube,  immerse  the  stoppered  end 
just  under  the  surface  of  some  water  in  a  convenient  ves- 
sel, and  pour  cool  water  on  the  upper  end.  What  takes 
place  ?  What  is  the  explanation  of  the  phenomenon  ?  Let 
cool,  uncork,  and  note  the  inrush  of  air.  If  the  cork  does 
not  come  out  easily,  force  a  pin  between  the  cork  and  the 
glass  and  withdraw  it. 

Optional  experiment. — In  a  small  evaporating  dish  evapo-  25 
rate  to  dryness  some  distilled  water.     Is  there  any  residue  ? 

Similarly  evaporate  to  dryness  some  sample  of  natural 
water.     Is  there  a  residue  ? 


CHAPTER  II 

EXPERIMENTS  ILLUSTRATING  THE  FUNDAMENTAL  QUAN- 
TITATIVE LAWS   OF  CHEMICAL  CHANGE 

33  NOTE. — Study  with  special  care  the  quantitative  relations  in  the  ex- 
periments of  this  chapter.  In  all  the  measurements  of  quantity  which 
you  make,  whether  in  this  work  or  in  the  work  of  subsequent  chapters, 
try  to  make  an  estimate  of  the  uncertainty  which  is  necessarily  in- 
volved in  the  measurements  by  reason  of  the  conditions  in  which  you 
work.  In  some  of  the  problems  it  will  be  important  to  make  at  least 
two  measurements  of  the  same  quantity,  in  order  to  show  how  much 
uncertainty  is  thus  involved.  As  the  work  advances,  after  you  have 
studied  the  primary  topic  which  is  illustrated,  give  some  thought  to 
the  topics  already  passed,  which  may  find  secondary  illustration  by  the 
experiment  in  hand,  especially  as  to  these  general  laws,  and  also  as 
to  the  kind  of  reaction  involved,  and  other  definitions  presented  in 
Chapter  I. 

Have  care  always  to  state  in  your  notes  the  specific  topic  to  be 
illustrated,  and,  when  practicable,  the  specific  experimental  problem  to 
be  solved ;  then  describe  your  method  of  solution,  endeavoring  to  give 
the  essential  features,  apparatus,  incidental  observations,  etc. ;  then,  as  a 
rule,  present  the  data  of  observation,  carefully  labeled,  the  calculations, 
if  any,  and  the  final  result,  with  your  conclusions  therefrom. 

In  recording  data,  be  sure  that  your  notes  include  all  original 
observations.  For  example,  you  are  to  determine  the  weight  of  a  sub- 
stance contained  in  a  dish ;  you  do  so  by  determining  the  weight  of 
the  dish  with  its  contents,  and  the  weight  of  the  dish  alone,  the  differ- 
ence between  these  being  the  weight  sought.  Now,  the  important  point 
is  to  record  in  your  notes,  not  simply  this  difference,  but  the  original 
weights  which  by  subtraction  give  the  desired  value. 

Notes  should  be  written  in  the  laboratory,  during  the  progress  of 
the  experiment,  and  quantitative  data  should  be  recorded  at  once.  Do 
not  rush  through  an  experiment  and  then  try  to  write  up  your  notes 
from  memory,  perhaps  outside  the  laboratory.  Do  not  delay  recording 
results  until  you  have  learned  whether  they  are  good.  Put  them  all 
24 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       25 

down,  and  later  mark  "  erroneous,"  if  necessary.  Do  not  be  discouraged 
if  the  result  at  first  trial  is  unsatisfactory.  You  will  often  need  to 
perform  an  experiment  once  to  learn  how  to  do  it,  and  need  to  repeat 
for  successful  results.  It  is  well  to  bear  in  mind  that  practical  chem- 
istry is  more  or  less  a  handicraft,  ancl  that  you  will  surely  fail  to  get 
good  return  for  your  time  and  labor  unless  experiments  are  performed 
carefully  as  well  as  studiously. 

Make  it  a  rule  to  read  through  the  directions  for  the  whole  experi- 
ment before  you  start  upon  its  performance. 


1.   The  Law  of  Persistence  of  Mass 

A.  Preliminary. — Some  apparent  contradictions  : 

(a)  Place  about  1  gram  of  mercury  sulphocyanate  in  34/1 
&  small  evaporating   dish,  counterpoise  the  dish  and  its 
contents  on  the  balance,  ignite  the  substance  by  a  match 

or  a  hot  iron  wire.  Describe  the  phenomenon,  and  note  the 
effect  on  the  equilibrium  of  the  balance.  Had  you  made 
the  experiment  without  using  the  balance,  what  would  you 
have  inferred  as  to  the  effect  of  the  change  on  the  quantity 
of  substance  ? 

(b)  An  experiment  for  the  teacher  to  perform  before  the  34/2 
class. — Burn  a  taper,  or  alcohol  in  a  small  lamp,  in  such 
manner  as  to  collect  and  weigh  the  products  of  combustion. 
This  may  be  conveniently  done  as  follows :  Suspend  the 
taper  or  very  small  lamp  (which  can  be  made  from  a  short 
test-tube,  a  cork,  and  a  piece  of  wicking)  from  the  lower 
end  of  a  student-lamp  chimney,  to  the  upper  end  of  which 

is  fitted  a  perforated  cork  carrying  a  train  of  four  absorp- 
tion tubes  ;  the  first  two  of  these  are  filled  with  fragments 
of  sodium  hydroxide,  and  the  last  two  with  fragments  of 
calcium  chloride ;  to  the  farther  end  of  the  train  is  at- 
tached a  rubber  hose  leading  to  a  filter  pump  or  to  an 
aspirator ;  the  whole  apparatus — lamp,  chimney,  and  absorb- 
ing train — is  then  suspended  from  the  arm  of  a  suitable 
balance  and  counterpoised.  When  this  is  ready,  start  the 
pump  which  draws  a  current  of  air  through  the  apparatus, 


26          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

carrying  with  it  the  products  of  combustion  into  the  tubes, 
where  they  are  retained.  Light  the  lamp  and  allow  it  to 
burn  fifteen  or  twenty  minutes,  noting  the  effect  on  the 


FIG.  1.— Diagram  of  apparatus  for  Exp.  34/2.     L,  alcohol  lamp  ;    C,  lamp 
chimney;   TI,  T*  Ta,  and  T4,  absorption  tubes. 

equilibrium  of  the  balance.  How  does  the  weight  of  the 
products  of  combustion  compare  with  the  weight  of  the 
material  burned?  (Fig.  1.) 

34/3  An  alternative  form  of  apparatus  for  this  experiment 
may  be  more  simply  provided  as  follows  :  Make  a  cylinder 
of  wire  gauze  which  shall  fit  closely  in  the  upper  half  of 
the  student-lamp  chimney ;  fit  the  lower  end  with  a  cork, 
through  which  several  holes  are  bored,  and  to  which  a  short 
piece  of  taper  may  be  attached  (see  Fig.  2),  or,  preferably, 


QUANTITATIVE  LAWS  OF   CHEMICAL  CHANGE      27 

suspend  the  little  alcohol  lamp  as  in  Fig.  1.     Fill  the  gauze 
cylinder  with  fragments  of  sodium  hydroxide,  and  suspend 
the  whole  by  a  loop  of  wire  from  the  arm  of  the  balance. 
Light  the  lamp  or  the  taper.     Although  the 
products  of  combustion  are  not  so  fully  re- 
tained as  in  the  preceding  form,  the  gain  in 
weight  is  made  evident  by  burning  for  a  few 
minutes. 

EXPLANATORY  NOTE.— The  alcohol  and  the  candle 
contain  carbon  and  hydrogen  as  elementary  constitu- 
ents. These  in  the  process  of  burning  combine  chem- 
ically with  the  oxygen  of  the  air,  forming  as  products 
gaseous  carbon  dioxide  and  hydrogen  oxide — i.  e.,  wa- 
ter. These  products  are  carried  into  the  tubes,  where 
the  carbon  dioxide  is  retained  by  the  sodium  hydrox- 
ide, and  the  water  is  retained  partly  by  condensing  to 
liquid  form,  and  partly  by  the  strongly  hygroscopic 
substance,  calcium  chloride.  The  products  of  the 
combustien,  therefore,  weigh  more  than  the  material 
burned  by  just  the  weight  of  the  oxygen  taken  into 
combination  from  the  air. 

All  the  ordinary  fuels  likewise  contain  carbon  and 
hydrogen ;  therefore  the  products  of  ordinary  combus- 
tion are  carbon  dioxide  and  water,  and  combustion  itself  is  simply  an 
instance  of  chemical  action  accompanied  by  heat  and  light.     (Compare 
with  Exps.  13,  15/2  and  15/3.) 

B.  To  illustrate  the  law: 

(1)  Eecall  or  repeat  Exps.  13/2a,  and  15/lt 

(2)  In  a  gas  generator  (see  Appendix,  6)  fitted  with  a  34/5 
thistle-tube  and  a  delivery  tube  place  a  charge  of  marble 

(i.  e.,  calcium  carbonate,  symbol  CaC03)  in  small  lumps, 
with  enough  water  to  seal  the  end  of  the  thistle-tube ;  in 
another  vessel  (a  bottle  or  a  deep  beaker)  place  a  strong 
solution  of  sodium  hydroxide  ;  in  a  third  (a  small  beaker), 
some  concentrated  hydrochloric  acid  and  a  glass  rod. 
Counterpoise  the  three  vessels  with  their  contents  on  the 
heavier  balance  (see  Appendix,  1,  A).  Cautiously  turn  the 
acid,  a  few  drops  at  a  time,  into  the  generator  (observe 


28          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

what  takes  place),  letting  the  reaction  go  on  slowly  through 
a  measured  interval  of  time  while  the  delivery  tube  opens 
into  the  air,  and  until  the  effect  on  the  equilibrium  is  un- 
mistakable. (What  is  the  effect  ?)  Then  drop  the  delivery 
tube  into  the  second  vessel  so  that  the  gas  bubbles  through 
the  solution ;  again  counterpoise,  and  continue  the  reac- 
tion at  about  the  same  rate,  and  during  the  same  length 
of  time  as  before ;  then  again  note  the  effect  on  the  equi- 
librium. 

Secondary  observation. — To  show  that  an  invisible  gas, 
quite  different  from  air  and  not  before  present,  is  produced 
by  this  change,  remove  the  material  from  the  balance,  drop 
the  delivery  tube  into  a  clean  beaker  or  bottle,  partly 
covered  by  a  glass  plate  (see  Appendix,  19,  V),  and  pour  a 
little  more  acid  into  the  generator.  After  the  effervescence 
has  continued  a  few  seconds,  slide  the  plate  to  one  side  and 
plunge  a  lighted  match  into  the  bottle.  The  gas  produced 
is  carbon  dioxide,  symbol  C02. 

EXPLANATORY  NOTE. — This  experiment,  owing  to  the  limitations  in 
weighing,  can  give  but  crude  quantitative  results,  showing  simply  that 
the  balance,  which  gives  no  indication  of  differences  less  than  0.2  or  0.3 
of  a  gram,  indicates  unmistakable  loss  of  weight  in  the  first  condi- 
tions, but  no  loss  in  the  second,  although  the  reaction  goes  on  as  in 
the  first, 

The  chemical  name  of  marble  is  calcium  carbonate,  symbol  CaC08. 
It  is  a  salt  derived  from  the  metal,  calcium,  and  carbonic  acid,  symbol 
H2C03.  By  the  action  of  hydrochloric  acid  on  this  substance,  calcium 
chloride,  another  salt,  symbol  CaCla,  is  produced,  and  carbonic  acid. 
The  latter  substance  breaks  up  at  once  into  carbon  dioxide,  symbol 
C03,  and  water,  symbol  H20.  The  carbon  dioxide  passes  into  the 
atmosphere  as  an  invisible  gas,  the  water  adds  itself  to  the  rest  of  the 
water,  and  the  calcium  chloride  remains  in  solution.  These  two  reac- 
tions are  expressed  in  equation  form  as  follows : 

(1)  CaC03  +  2HC1  =  CaCla  +  HaCO». 

(2)  HaCOs  =  C03  +  H20. 

Sodium  hydroxide,  symbol  NaOH,  is  a  base  (see  Part  I,  30/a),  and 
when  the  carbon  dioxide  comes  in  contact  with  its  solution  in  the  sec- 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       29 

ond  bottle  the  two  substances  combine  and  another  salt  is  produced, 
namely,  sodium  carbonate,  symbol  Na2C03.  This  remains  in  solution. 
The  following  equation  expresses  this  reaction  : 

SNaOH  +  C02  =  Na3COs  +  H20. 


2.  The  Law  of  Fixed  or  Definite  Proportions 

(a)  Evaporate  to  dryness  a  few  drops  of  hydrochloric  37 
acid  solution  in  the  small  evaporating  dish,  heating  gently 
with  the  caution  necessary  in  this  operation  (see  Appendix 
12).     Acid  of  a  good  degree  of  purity  is  needed. 

(b)  Likewise  evaporate  a  few  drops  of  ammonium  hy- 
droxide solution.     Describe  the  results. 

(1)  Carefully  weigh  to  tenths  of  a  gram  the  small 
porcelain  dish  with  a  short  glass  rod,  both  articles  being 
clean  and  dry. 

[It  will  be  advantageous  to  have  two  or  even  three 
weighed  dishes  to  use.  They  may  be  distinguished  by 
scratches  on  their  edges  made  with  a  file.] 

With  some  suitable  measure  (a  test-tube  with  a  slip  of 
gummed  paper  or  a  file  scratch  on  its  side  will  serve, 
although  a  burette  or  graduated  pipette  is  better)  take  two 
equal  volumes  of  the  ammonium  hydroxide  solution,  pour- 
ing them  into  a  weighed  dish.  Exactly  neutralize  this 
liquid  with  the  hydrochloric  acid  solution,  using  litmus 
paper  as  indicator,  and  adding  the  acid  drop  by  drop,  stir- 
ring after  each  addition,  until  the  paper  just  turns  per- 
manently pink.  Note  carefully  the  volume  of  acid  used. 
Evaporate  the  contents  of  the  dish  to  dryness  on  the  water- 
bath  ;  this  is  facilitated  by  frequent  stirring  toward  the  end 
of  the  operation.  Let  cool,  and  determine  the  weight  of 
the  salt  obtained.  How  will  you  make  sure  that  the  salt 
is  completely  dried  ? 

Redissolve  the  salt,  using  very  little  water;  filter  if  neces- 
sary, and  crystallize.  Dry  the  crystals  on  filter  paper,  and 
test  them  with  blue  and  with  red  litmus  paper  slightly  wet. 


30          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

(2)  Take  the  same  volume  of  hydrochloric  acid  which 
was  used  in  (1),  add  to  it  only  one  measureful  of  ammonium 
hydroxide,  evaporate,  and  weigh  as  before  the  salt  obtained. 
Eedissolve,  filter,  and  crystallize  this  salt.    Test  the  crystals 
with  red  and  with  blue  litmus  paper. 

(3)  Take  again  the  same  volume  of  acid  as  previously 
used,  add  to  it  three  measurefuls  of  ammonium  hydroxide, 
evaporate,  and  weigh  as  before. 

Eedissolve,  filter,  and  crystallize   this  salt.     Test  the 
crystals  with  red  and  with  blue  litmus  paper. 

38  QUESTIONS. — Are  the  three  portions  of  salt  thus  obtained  different 
samples  of  the  same  substance,  or  are  they  different  substances?    What 
is  the  ratio  between  the  quantities  of  salt  obtained  in  the  three  cases  ? 
Have  you  any  evidence  that  hydrochloric  acid  or  ammonium  hydroxide 
passes  off  during  the  evaporation,  in  (1)  ?  in  (2)  ?  in  (3)  ?    What  is  the 
logic  of  the  experiment  ?    Reason  it  out  fully.     Is  heat  liberated  when 
hydrochloric  acid  and  ammonium  hydroxide  are  mixed  ? 

39  EXPLANATORY  NOTE. — The  salt  obtained  by  the  combination  of 
hydrochloric  acid  and  ammonium  hydroxide  (symbol  NH4OH,  a  base) 
is  named  ammonium  chloride,  symbol  NH4C1,  and  the  reaction  is  thus 
expressed :    Hydrochloric    acid    and    ammonium   hydroxide   produce 
ammonium  chloride  and  water ;  or  in  equation  form, 

HC1  +  NH4OH'=  NH4C1  +  H2O. 


3.  The  Law  of  Multiple  Proportions 

40/a  (a)  Take  of  iodine  and  of  mercury  in  the  ratio  of  252 
parts  by  weight  of  the  former  and  199  of  the  latter ;  for 
the  actual  experiment  weigh  out  accurately  (in  some  glass 
vessel,  as  both  substances  attack  metals)  6.30  grams  of 
iodine,  and  5.00  grams  of  mercury.  Transfer  the  mer- 
cury to  a  mortar  (previously  weighed  with  its  pestle  on 
the  heavier  balance).  Add  a  few  drops  of  alcohol,  then  a 
small  portion  of  the  iodine,  and  rub  gently  with  the  pes- 
tle ;  then  add  another  portion  of  iodine,  and  rub ;  and  so 
on  until  all  the  iodine  is  used  and  the  whole  is  thoroughly 
mixed. 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE      31 

It  is  well  to  keep  the  mixture  slightly  moist  with  alcohol  during 
only  the  first  stages  of  the  operation,  in  order  to  avoid  overheating, 
otherwise  there  may  occur  a  slight  flash  in  the  mortar,  accompanied  by 
the  fusion  of  the  substance.  If  this  happens,  it  is  better  to  clean  the 
mortar  (use  sand  to  scour),  and  start  the  experiment  anew.  Avoid  in- 
haling the  fumes  of  iodine,  and  protect  the  hand,  if  desired,  with  a 
fold  of  the  towel.  Iodine  stains  may  be  removed  with  sodium  sulphite 
or  ammonium  sulphide. 

Persistent  rubbing  may  be  necessary  even  after  the  sub- 
stances seem  well  mixed.  The  operation  when  completed 
should  yield  a  bright-red  powder,  mercuric  iodide,  symbol 
HgI2. 

Weigh  the  mortar  and  contents  on  the  heavier  balance. 

Take  out  a  small  sample  and  apply  alcohol  to  it  in  a  40/1 
test-tube.  [The  alcohol  should  not  be  colored  by  the 
iodine  ;  if  it  is  so  colored,  continue  the  rubbing.]  Warm 
the  alcohol  to  gentle  boiling,  having  care  that  the  alcohol 
vapor  is  not  ignited  by  the  flame ;  set  aside  to  cool.  The 
amorphous  powder  dissolves  in  hot  alcohol,  and  deposits 
on  cooling  in  crystalline  scales,  sometimes  bright  scarlet, 
sometimes  yellow  (allotropic  forms). 

Sublime  another  small  portion  of  the  red  powder  in  a  40/2 
dry  test-tube,  note  the  red  and  yellow  sublimate  (allotropic 
forms) ;  rub  the  yellow  with  a  glass  rod.    Note  the  crystal- 
line residue  after  fusion. 

(V)  Take  5.60  grams  of  mercuric  iodide  obtained  in  40/b 
(«),  which  is  equal  to  ^  (6.3  +  5)  and  2.50  grams  of  mer- 
cury. Add  the  mercury  in  small  portions  at  a  time  to 
the  mercuric  iodide  in  a  mortar,  rubbing  thoroughly  after 
each  addition.  This  should  yield  a  greenish-yellow  powder 
(mercurous  iodide,  symbol  Hgl).  If  the  color  is  not  satis- 
factory, continue  the  rubbing  and,  perhaps,  allow  to  stand 
for  twenty-four  hours. 

Weigh  the  mortar  and  contents  on  the  heavier  bal- 
ance. 

Treat  a  small  portion  as  in  (a)  with  boiling  alcohol.   40/3 
Does  it  dissolve  ? 


32          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

40/4         Sublime  another  portion ;  note  the  character  of  the  sub- 
limate and  the  residue  after  heating. 

40/5          EXPLANATORY  NOTE. — Mercurous  iodide  is  insoluble  in  hot  alcohol 
and  decomposes  on  heating  into  mercuric  iodide  and  mercury. 

QUESTIONS. — How  do  you  differentiate  between  mercury  and  iodine 
mixed,  and  mercuric  iodide!  between  mercuric  iodide  and  mercurous 
iodide  f  between  mercuric  iodide  and  mercury  mixed,  and  mercurous 
iodide  f  How  does  the  weight  of  the  mercuric  iodide  obtained  com- 
pare with  that  of  the  mercury  and  iodine  used  1  What  becomes  of  the 
alcohol  f  How  does  the  weight  of  the  mercurous  iodide  compare  with 
that  of  the  mercuric  iodide  and  the  mercury  used  ?  What  is  the  ratio 
between  the  quantities  of  mercury  in  the  two  substances  reckoned  for 
constant  quantity  of  iodine  ?  between  the  quantities  of  iodine,  reckoned 
•  for  constant  quantity  of  mercury  ?  What  is  the  logic  of  the  experi- 
ment f  Show  clearly  that  it  is  not  contradictory  to  Law  2.  What 
does  Law  2  affirm  in  regard  to  these  two  reactions  ?  What  does  Law 
1  affirm  with  regard  to  them  ?  Is  heat  liberated  in  the  reaction  be- 
tween mercury  and  iodine  f 


4.  The  Law  of  Equivalent  Proportions* 

41  General  problem. — To  investigate  the  relation  between 
those  quantities  of  different  substances  which  produce 
equal  chemical  -effects. 

Specific  illustrative  problem. — A.  To  determine  the  rela- 
tion between  the  quantities  of  oxygen  which  combine 
respectively  (1)  with  2.40  grams  of  magnesium,  and  (2) 
with  6.50  grams  of  zinc. 

B.  To  determine  the  relation  between  the  quantities  of 
hydrogen  liberated  from  hydrochloric  acid  respectively  (3) 
by  2.40  grams  of  magnesium,  and  (4)  by  6.50  grams  of 
zinc. 


*  Inasmuch  as  the  experiment  under  this  topic  involves  the  meas- 
urement of  gas- volume,  the  instructor  may  prefer  to  introduce  the  laws 
of  Boyle  and  of  Charles,  Chapter  IV,  at  this  point.  The  writer  prefers 
to  give  them  simply  as  arbitrary  rules  and  to  study  them  later,  rather 
than  to  interrupt  the  logical  development  of  this  chapter. 


QUANTITATIVE  LAWS  OF  CHEMICAL   CHANGE       33 

A  1 

To  determine  the  quantity  of  oxygen  which  combines  41/1 
with  2.40  grams  of  magnesium :  Recall  Exp.  15/2.  Weigh 
to  hundredths  of  a  gram  a  porcelain  crucible  with  its  lid, 
clean  and  dry.  Weigh  out  exactly  1.00  gram  of  magnesium 
ribbon.  Breaking  this  into  small  pieces,  transfer  the  whole 
to  the  crucible.  Support  the  latter,  covered  by  its  lid,  on 
the  pipe-stem  triangle  and  iron  stand  (see  Appendix,  11). 
Apply  heat,  slowly  at  first,  then  the  full  heat  of  the  flame. 
Raise  the  lid  slightly  from  time  to  time  to  see  what  is 
taking  place  and  to  let  air  in,  but  avoid  losing  any  of  the 
white  smoke.  When  the  danger  of  this  is  passed,  remove 
the  lid  and  continue  the  heating  about  fifteen  minutes. 
When  the  crucible  is  cool,  weigh  it  with  its  lid  and  con- 
tents to  hundredths.  To  make  sure  that  the  reaction  is 
complete,  heat,  cool,  and  weigh  again.  When  heated,  the 
magnesium  combines  with  the  oxygen  of  the  air  and  the 
product  is  magnesium  oxide,  MgO.  Calculate  from  the 
mass  of  oxygen  which  combines  with  1.00  gram  of  mag- 
nesium what  mass  combines  with  2.40  grams  of  the  same. 
(Upon  what  law  is  this  calculation  based  ?)  At  least  two 
determinations  of  this  value  should  be  made. 

Secondary  items. — Describe  the  phenomenon  seen  and  41/a 
the  substance  produced.  Does  the  reaction  evolve  heat  ? 
Does  magnesium  oxide  dissolve  in  hot  water  ?  Test  with 
red  litmus  paper.  Does  it  dissolve  in  dilute  sulphuric  acid  ? 
Boil  it  in  the  crucible  or  dish  with  a  very  little  of  the  dilute 
acid,  filter,  and  crystallize  the  salt,  magnesium  sulphate, 
MgS04  (compare  Exp.  17/2).  How  does  the  reaction  be- 
tween magnesium  oxide  and  sulphuric  acid,  symbol  H2S04, 
differ  from  that  between  magnesium  and  the  same  acid  ? 

An  Alternative  Method 

This  method  involves  making,  first,  magnesium  iodide,  Mgla,  then    41/b 
heating  this  substance,  by  which  it  is  decomposed  into  iodine  and  mag- 


34          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

nesium,  and  the  latter  is  converted  into  the  oxide,  MgO,  all  without  loss 
of  substance  other  than  the  iodine.  The  final  result  is  the  same  as  in 
41/i,  but  it  is  brought  about  with  less  elevation  of  temperature. 

Weigh  to  hundredths  a  small  evaporating  dish  with  a 
short  glass  rod.  Weigh  out  carefully  0.50  of  a  gram  of 
magnesium,  and  place  this  in  the  dish.  Weigh  out  about 
5  grams  of  iodine.  Pour  on  the  magnesium  enough  alco- 
hol to  cover  it.  Then  add  the  iodine,  a  little  at  a  time, 
stirring  constantly.  With  a  little  care  the  reaction  may  be 
so  controlled  that  the  heat  evolved  shall  not  cause  spatter- 
ing and  consequent  loss  of  material.  When  the  magnesium 
is  entirely  acted  upon,  heat  the  dish  and  contents  on  the 
water-bath  until  only  a  thick,  siruplike  mixture  is  left. 
Then  transfer  the  dish  to  the  iron  ring  and  heat  with  a 
very  small  flame,  holding  the  burner  in  the  hand  (as  before 
directed  for  careful  evaporation ;  see  Appendix,  12),  and 
stirring  constantly.  Continue  this  until  the  danger  of 
spattering  is  past,  then  apply  the  full  heat  of  the  flame. 
As  this  causes  iodine  fumes,  it  may  be  necessary  to  perform 
this  part  of  the  experiment  in  the  hood.  Continue  the 
heating  for  a  few  minutes  after  the  iodine  has  entirely  dis- 
appeared. Finally  let  cool,  and  weigh  the  dish  and  con- 
tent, which  is  magnesium  oxide,  a  fine  powder  only  slightly 
brown  in  tint.  The  calculations  are  the  same  as  in  the 
first  method. 

A2 

41/2         To  determine  the  quantity  of  oxygen  which  combines 
with  6.50  grams  of  zinc  : 

It  is  impracticable  to  do  this  by  direct  combustion,  as  in  the  mag- 
nesium experiment.  The  method  is  to  act  on  zinc  with  nitric  acid,  pro- 
duce zinc  nitrate,  dry  this,  then  ignite  it  and  thus  produce  zinc  oxide 
without  loss  of  other  than  volatile  material.  Refer  to  Exps.  15/3  and  16/2. 

Weigh  a  small  evaporating  dish  with  a  short  glass  rod 
to  hundredths  of  a  gram.  Weigh  out  2.00  grams  of  granu- 
lated zinc.  Transfer  the  latter  to  the  dish.  Pour  a  drop 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       35 

or  two  of  nitric  acid  down  the  rod,  letting  it  come  slowly 
in  contact  with  the  zinc.  (Remember  that  nitric  acid  is 
very  corrosive.)  When  the  first  violent  reaction  is  over, 
add  a  few  drops  more  of  acid,  and  so  on  until  the  zinc  is 
completely  dissolved  with  the  least  acid  that  will  serve. 
Evaporate  the  contents  of  the  dish  to  dryness  on  the  water- 
bath.  The  evaporation  may  be  performed  more  quickly, 
but  only  with  closer  attention,  by  holding  the  burner  in  the 
hand,  having  the  flame  low,  and  applying  just  enough  heat 
to  keep  the  liquid  gently  boiling,  until  there  is  danger 
of  spattering,  and  then  not  enough  heat  to  cause  the  for- 
mation of  bubbles  (see  Appendix,  12).  When  the  salt  is 
thoroughly  dry,  increase  the  heat,  and  finally  give  it  the 
full  flame  for  about  fifteen  minutes.  When  the  reaction  is 
finished,  let  the  dish  cool,  and  weigh  it  with  its  contents 
to  hundredths  of  a  gram.  The  product  is  zinc  oxide.  To 
make  sure  that  the  reaction  is  complete,  heat,  cool,  and 
weigh  again.  From  the  mass  of  oxygen  which  combines 
with  2.00  grams  of  zinc,  calculate  what  mass  combines 
with  6.50  grams  of  the  same.  At  least  two  determinations 
of  this  value  should  be  made. 

Secondary  items, — Describe  the  reaction  between  zinc  and  41 /c 
nitric  acid.     Is  heat  evolved  ?    What  takes  place  when  zinc 
nitrate  is  heated  ?    Does  zinc  oxide  dissolve  in  water  ?  in 
dilute  sulphuric  acid  ?     Optional  experiment :  Filter,  and 
crystallize  the  zinc  sulphate  (see  Exp.  17/8). 

How  does  the  reaction  between  zinc  oxide  and  sulphuric 
acid  differ  from  that  between  zinc  and  the  same  acid? 
What  is  obtained  by  the  action  of  hydrochloric  acid  on 
zinc  oxide  ? 

Summary. — Compare  with  each  other  the  individual  41/d 
quantitative  results  with  magnesium,  also  those  with  zinc ; 
then  compare  the  average  of  the  first  with  the  average  of 
the  second.  What  is  the  conclusion  as  to  the  masses  of 
oxygen  which  combine  respectively  with  2.40  grams  of 
magnesium  and  with  6.50  grams  of  zinc  ? 


36          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

B  3 

41/3  To  measure  .by  volume  and  calculate  into  weight  the 
quantity  of  hydrogen  liberated  from  hydrochloric  acid  by 
2.40  grams  of  magnesium  : 

(a)  To  measure  the  capacity  of  the  collecting  bottle, 
No.  x  (a  bottle  with  glass  stopper  holding  about  2,500  c.c.): 
Fill  the  tank  with  water,  which  should  be  brought  to  the 
temperature  of  the  room,  if  necessary  by  heating  portions 
in  the  iron  vessel.  Fill  the  collecting  bottle  completely 
and  put  the  stopper  in  place.  Measure  the  volume  of  this 
water  in  cubic  centimeters ;  this  may  be  done  by  pouring, 
without  loss,  into  a  graduated  cylinder,  or,  if  such  vessel  is 
lacking,  as  follows  :  Fill  a  graduated  flask  repeatedly  from 
the  bottle  (one  holding  750  c.c.  is  convenient),  and  weigh, 
in  a  vessel  not  unnecessarily  large  or  heavy,  the  last  residue 
which  is  insufficient  again  to  fill  the  flask ;  the  weight  of 
the  water  in  grams  may  be  taken  with  only  inconsiderable 
error  as  its  volume  in  cubic  centimeters.  Determine  thus 
the  capacity  at  least  twice.  The  variations  should  not  be 
more  than  one  or  two  cubic  centimeters. 

[Why  not  weigh  at  once  the  bottle  filled  with  water  ?] 
41/3b  (b)  To  generate  the  gas  :  Weigh  out  carefully  2.40 
grams  of  magnesium  ribbon,  transfer  without  loss  to  the 
gas  generator  (see  Appendix,  6).  Add  water  just  sufficient 
to  seal  the  thistle-tube ;  test  for  leakage  by  blowing  in  the 
exit  end  of  the  delivery  tube  until  the  water  rises  four  or 
five  inches  in  the  thistle-tube,  then  pinching  the  rubber 
hose,  or  closing  the  end  of  the  tube  with  the  tongue.  The 
column  of  water  should  maintain  its  height,  or  sink  only 
slowly.  A  film  of  water  between  stopper  and  glass  will 
help  to  prevent  leakage,  or,  as  a  last  resort,  the  stopper  may 
be  sealed  with  vaseline  or  with  paraffin. 

Have  some  strong  hydrochloric  acid  in  a  beaker.  It 
will  be  found  convenient  to  let  a  test-tube  lie  in  the  bulb 
of  the  thistle-tube ;  it  may  be  used  like  a  rod  to  aid  in 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       3? 

pouring  from  the  beaker,  and  the  rounded   end  makes  a 
kind  of  valve. 

(c)  To  collect  and  measure  the  gas  :  Fill  the  collecting  41/3c 
bottle  with  water,  put  in  the  stopper,  invert  in  the  tank, 
remove  the  stopper,  incline  the  bottle  so  that  it  rests  on  the 
wall  of  the  tank  and  slip  into  its  mouth  the  bent  delivery 
tube  (compare  Appendix,  19,  I).  Pour  acid,  a  little  at  a 
time,  into  the  thistle-tube  until  no  more  gas  is  generated. 
As  much  heat  is  liberated  in  this  reaction,  it  is  well  to  set 
the  generator  down  into  the  water  of  the  tank.  Ascertain 
now  or  later  the  volume  in  cubic  centimeters  of  the  acid 
turned  in. 

When  the  effervescence  ceases,  raise  the  bottle  so  that 
the  water  within  and  without  is  as  nearly  as  practicable  at 
the  same  level,  withdraw  the  delivery  tube,  insert  the  stop- 
per under  water,  and  remove  the  bottle  from  the  tank. 
Measure  the  volume  of  the  water  left  in  the  bottle,  and 
calculate  the  volume  of  the  gas  collected. 

Observe  the  temperature  of  the  water  in  the  tank,  which 
should  be  that  of  the  room,  so  that  it  may  be  safely  assumed 
that  the  temperature  of  the  gas  is  the  same. 

Observe  by  the  barometer  the  pressure  of  the  atmos- 
phere (see  Appendix,  No.  15  B). 

Take  note  that  hydrogen  with  air  may  make  a  danger- 
ously explosive  mixture  ;  therefore  have  great  care  that  the 
hydrogen  is  not  brought  near  a  flame. 

Calculations.      (See  Appendix,  20.)— The    data  of  this  41/8d 
problem  are : 

The  weight  of  metal  used ; 

The  total  capacity  of  the  bottle ; 

The  volume  of  acid  turned  in  (how  is  this  used  ?) ; 

The  volume  of  water  left  in  the  bottle ; 

The  temperature  and  pressure  of  the  gas. 

From  these  is  first  calculated  the  volume  of  the  gas 
generated,  measured  in  cubic  centimeters  at  the  observed 
temperature  and  pressure. 
20 


38          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

Now,  since  change  of  temperature  and  change  of  pres- 
sure cause  change  in  the  volume  of  gases,  it  is  important 
that  observed  volumes,  in  order  to  be  comparable,  should 
be  reduced  to  standard  conditions  of  temperature  and  pres- 
sure. It  is  customary  to  use  as  standards  0°  C.  for  tem- 
perature and  760  millimeters  of  mercury  column  in  the  ba- 
rometer for  pressure.  The  method  of  reducing  observations 
to  the  standards  may  be  taken  arbitrarily  now,  to  be  ex- 
plained in  Chapter  IV.  The  observed  volume  is  reduced 
to  volume  at  0°  by  applying  the  law  that  "  a  volume  of  gas 
at  0°  increases  by  -^  of  itself  for  each  degree  of  rise  in 
temperature,  pressure  remaining  unchanged."  The  observed 
volume  is  reduced  to  volume  at  760  mm.  by  multiplying  by 
the  observed  pressure  in  millimeters  and  dividing  by  760 ; 
but  since  the  gas  is  collected  and  measured  over  water,  it  is 
saturated  with  water  vapor,  and  the  observed  pressure  is 
made  up  of  the  true  pressure  of  the  gas  plus  the  pressure 
of  the  vapor  at  the  given  temperature.  The  pressure  or 
tension  of  the  water  vapor  at  different  temperatures  is 
obtained  by  observation,  and  given  in  tables  accessible  in 
books  of  reference  ;  this  value  for  the  ordinary  temperature 
of  20°  is  17  mm.,  and  may  be  subtracted  from  the  observed 
pressure  as  a  slight  correction.  (See  Appendix  22.) 

The  volume  of  gas  generated,  thus  brought  to  standard 
conditions,  is  finally  calculated  into  weight,  by  aid  of  the 
fact  that  one  liter  of  hydrogen  at  0°  and  760  mm.  weighs 
0.0899  of  a  gram.  Does  the  fact  that  the  hydrogen  collected 
in  the  bottle  is  mixed  with  air  coming  from  the  generator 
affect  the  problem  ? 

At  least  two  fairly  concordant  determinations  should  be 
made  of  the  hydrogen  by  magnesium. 

B  4 

41/4  To  measure  by  volume  and  calculate  into  weight  the 
quantity  of  hydrogen  liberated  by  6.50  grams  of  zinc  (com- 
pare Exp.  17/j) :  Proceed  as  in  B  3,  (£)  and  (c),  using  6.50 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE       39 

grams  of  granulated  zinc.     At  least  two  fairly  concordant 
determinations  of  this  value  should  he  made. 

Summary.— Compare  with  each  other  the  individual  41/5 
results  from  magnesium ;  also  those  from  zinc  ;  then  the 
average  of  the  first  with  the  average  of  the  second.  What 
is  the  conclusion  as  to  the  quantities  of  hydrogen  liberated 
respectively  by  2.40  grams  of  magnesium  and  by  6.50  grams 
of  zinc  ?  Compare  the  results  in  A  and  B.  Are  the  masses 
of  magnesium  and  zinc  which  produce  equal  chemical  effect 
in  combining  with  oxygen  also  the  masses  which  produce 
equal  effect  in  liberating  hydrogen  ? 

5.  The  Law  of  Gas-volumetric  Proportions 

General  problem. — To  determine  the  proportions  by  vol- 
ume in  which  gaseous  substances  react. 

Specific  illustrative  problem. — To  investigate  the  propor-  47 
tion  by  volume  in  which  nitrogen  dioxide  reacts  (1)  with 
air  and  (2)  with  oxygen. 

EXPLANATORY  NOTE. — The  plan  of  work  under  this  topic  must  be  to 
state  first  the  fundamental  fact  involved,  and  to  let  the  experiment 
serve  rather  to  illustrate  the  practical  application  of  this  fact  to  the 
observations  in  hand. 

Nitrogen  dioxide,  symbol  NO  (named  also  nitric  oxide),  combines 
with  oxygen  on  contact  in  the  ratio  of  4  volumes  (gaseous)  of  the  former 
to  2  volumes  (gaseous)  of  the  latter,  forming  2  volumes  (gaseous)  of 
nitrogen  tetroxide,  symbol  Na04,  a  substance  which  is  soluble  in 
water.  Air  is  a  mixture  of  oxygen  and  nitrogen,  1  volume  of  the  for- 
mer to  4  volumes  of  the  latter.  Nitrogen  does  not  react  with  nitrogen 
dioxide. 

(a)  To  calibrate  two  gasometric  (i.  e.,  gas-measuring)  47/a 
tubes :  Use  two  test-tubes,  230  mm.  (9  in.)  long  and 
18  mm.  (f  in.)  wide,  and  as  a  unit  tube  one  about  44  mm. 
(If  in.)  long  and  10  mm.  (f  in.)  wide.  Divide  the  large 
tubes  into  portions  of  equal  capacity  by  filling  the  small 
tube  with  water,  pouring  its  content  into  the  large  tube, 
and  marking  the  level  of  the  water  with  a  rubber  band. 


40          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

47/b  (#)  To  prepare  nitrogen  dioxide  :  Put  into  the  generator 
a  charge  (to  about  half  fill)  of  ferrous  sulphate  (commer- 
cially known  also  as  copperas  and  as  green  vitriol)  in  small 
lumps,  with  water  just  enough  to  seal  the  thistle-tube. 
Have  strong  nitric  acid  with  a  rod  in  a  small  beaker.  Turn 
the  acid  a  little  at  a  time  into  the  generator.  Collect  the 
gas  over  water  in  the  small  collecting  bottles  (see  Appendix, 
19,  I),  rejecting,  as  probably  impure,  the  first  three  or  four 
bottlefuls ;  then  retain  for  use  stored  in  the  bottles.  Care- 
fully avoid  inhaling  the  gas;  also  handle  the  acid  with  care, 
as  it  is  very  corrosive. 

47/1  (1)  By  means  of  the  gasometric  tubes,  measure  out  vol- 
umes of  air  and  of  nitrogen  dioxide  in  the  ratio  of  5:2; 
pouring  the  latter  under  the  water  of  the  tank,  upward 
from  the  bottle  into  the  tube  (see  Appendix,  19,  II).  It  is 
advantageous  to  use  large  rather  than  small  quantities. 

Pass  the  content  of  one  tube,  under  water,  into  the 
other  (what  takes  place?),  and,  after  sufficient  interval, 
read  the  volume  of  the  residual  gas.  Eepeat  the  operation 
enough  to  get  fairly  concordant  results.  If  the  gas  is  pure 
and  the  measurements  well  made,  the  result  is  4  volumes 
in  proportion  to  the  5  and  the  2  which  were  taken ;  there- 
fore 3  volumes,  or  f  of  the  mixture,  disappear  in  the  reac- 
tion. (What  is  the  cause  of  this  contraction  ?) 

Take  a  measured  sample  of  the  residual  gas,  add  to  this 
a  measured  volume  of  air,  and  observe  the  contraction ;  if  it 
is  not  zero,  make  repeated  additions,  until  there  is  no 
further  contraction. 

Take  another  measured  sample  of  the  residual  gas,  add 
to  it  a  measured  volume  of  nitrogen  dioxide  ;  if  the  con- 
traction is  not.  zero,  continue  the  additions  until  it  is. 

Does  the  first  residual  gas  contain  oxygen  ?  Does  it  con- 
tain nitrogen  dioxide  ?  What  is  it  ? 

47/2  (2)  Measure  out,  as  in  (1),  volumes  of  oxygen  and  of 
nitrogen  dioxide  in  the  ratio  of  1  :  2.  Mix  them  and  meas- 
ure the  residual  volume  and  the  contraction. 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE      41 

If  there  is  a  residual  gas,  test  it  for  further  contraction 
by  repeated  additions  of  oxygen.  What  is  indicated  here 
by  contraction  or  absence  of  contraction  ? 

Likewise  test  the  residual  gas  for  further  contraction 
by  additions  of  nitrogen  dioxide.  What  does  contraction 
signify  here?  Why  are  observations  of  temperature  and 
pressure  unnecessary?  (For  a  convenient  form  of  record 
see  Prob.  8,  No.  65/6,  Part  I.) 

APPLICATIONS. — Measurement  of  contraction,  in  conditions  like  those  47/3 
just  indicated,  may  be  used  to  determine  the  real  volume  of  oxygen  or 
of  nitrogen  dioxide  in  a  given  sample — that  is,  the  purity  of  the  sample 
— provided  only  that  there  is  nothing  present  to  cause  contraction  in 
the  given  conditions,  except  these  two  substances.  It  is  only  necessary 
to  make  sure  that  the  substance  to  be  measured  has  been  entirely  used 
in  making  the  observed  contractions.  (How  is  this  made  sure  f)  Then 
the  volume  of  oxygen  actually  present  may  be  obtained  by  the  propor- 
tion 3  : 1 ::  observed  contraction  :  volume  of  oxygen  (why?);  and  the 
volume  of  nitrogen  dioxide  may  be  obtained  by  the  proportion  3:2:: 
observed  contraction  :  volume  of  nitrogen  dioxide  (why  ?).  Apply  this 
to  determine  the  percentage  purity  of  your  sample  of  nitrogen  dioxide 
and  of  oxygen.  Your  sample  of  the  first  will  be  of  good  quality  if  you 
reject  enough  to  have  it  free  from  nitrogen  coming  from  the  air.  Com- 
mercial oxygen  is  likely  to  be  impure,  also,  from  the  presence  of  ni- 
trogen. 

EXPLANATORY  NOTE. — The  reaction  by  which  the  nitrogen  dioxide  47/4 
is  produced  is  rather  complicated  for  complete  explanation  at  this 
stage ;  the  following  may  suffice  :  The  proximate  (see  No.  26,  Part  I) 
constituents  of  nitric  acid  are  water  and  nitrogen  pentoxide ;  the  latter 
very  readily  gives  up  a  portion  of  its  oxygen  to  other  substances,  and 
becomes  a  lower  oxide  of  nitrogen  (example  of  multiple  proportions), 
in  this  instance  the  dioxide  ;  the  agent  which  takes  this  oxygen  from 
the  nitrogen  pentoxide  is  ferrous  oxide,  a  proximate  constituent  of  the 
ferrous  sulphate ;  in  thus  taking  oxygen  this  substance  is  converted 
into  a  higher  oxide  of  iron — namely,  ferric  oxide  (example  of  multiple 
proportions). 

Substances  which  thus  give  up  the  whole  or  a  part  of  their  oxygen    48 
are  called  oxidizing  agents  ;  those  which  thus  take  on  oxygen  are  called 
reducing  agents. 


42          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


6.  The  Law  of  Persistence  or  Conservation  of  Energy 
applied  to  Chemical  Phenomena 

Heat  Disturbance  in  Chemical  Reactions 

(The  student  should  read  Nos.  50-55,  Part  I,  before 
undertaking  the  experiment.) 

50/1  THE  UNIT  OF  HEAT. — The  unit  of  quantity  which  is  used  in  meas- 
uring heat  is  defined  as  the  quantity  of  heat  which  raises  1  gram 
of  water  1°  in  temperature,  or,  strictly  defined,  from  0°  to  1°  C.,  but, 
as  more  commonly  used,  from  18°  to  19°.  This  unit  is  named  the 
calorie  (or  gram-calorie).  For  convenience,  a  unit  equal  to  1,000 
calories  is  often  used,  the  kilogram-calorie,  designated  by  the  abbre- 
viation, Cal.,  while  for  the  smaller  unit  the  abbreviation,  cal.,  is  used. 

50/2  The  quantity  of  heat  disturbance  is  most  simply  measured  when  the 
reaction  takes  place  quickly  and  in  water  solution,  as  in  the  neutrali- 
zation of  bases  and  acids.  The  result  is  commonly  reckoned  for  the 
combining  weights  in  grams  of  the  substances  used.  (Recall  in  what 
reactions  you  have  noted  the  liberation  of  heat.) 

50/3  Illustrative  problem. — To  determine  in  calories  the  quan- 
tity of  heat  liberated  in  neutralizing  125  grams  (its  com- 
bining weight)  of  oxalic  acid  with  ammonium  hydroxide, 
both  being  in  water  solution. 

Weigh  out  5.00  grams  of  oxalic  acid ;  dissolve  this  in 
100  c.c.  of  water  in  a  beaker.  Take  sufficient  ammo- 
nium hydroxide  solution  to  neutralize  this  acid,*  and  add 
enough  water  to  bring  its  volume  up  to  100  c.  c.  Have  the 
two  solutions  in  beakers,  and  at  a  temperature  not  far  dif- 
ferent from  that  of  the  room.  Observe  carefully  the  tem- 
perature of  each  solution.  Quickly  pour  one  into  the 
other,  stir  with  the  thermometer,  and  observe  the  resultant 
temperature.  (The  salt,  ammonium  oxalate,  may  be  read- 
ily crystallized  from  this  solution  by.  slight  concentration.) 

*  The  quantity  will  depend  on  the  strength  of  the  solution.  It  is 
recommended  that  the  instructor  determine  this  for  the  class,  or  assign 
it  to  some  student  as  a  problem. 


QUANTITATIVE  LAWS  OF  CHEMICAL  CHANGE   43 

Calculations. — In  dilute  solutions  it  may  be  assumed,  for  50/4 
calculations  such  as  these,  that  the  quantity  of  heat  needed 
to  raise  the  solution  one  degree  is  the  same  as  that  needed 
to  raise  the  water  which  it  contains  one  degree.  Sometimes 
the  weight  of  the  water  is  taken,  and  sometimes  the  volume 
of  the  solution  is  reckoned  as  if  it  were  pure  water.  The 
latter  method  is  somewhat  the  simpler.  In  this  experi- 
ment, the  two  volumes  being  equal,  the  temperature  of  the 
mixture  'would  be  the  mean  of  the  temperatures  before 
mixing,  if  no  heat  were  liberated.  The  difference  between 
this  mean  and  the  observed  resultant  temperature  is  the 
number  of  degrees  that  the  200  c.c.,  reckoned  as  so  many 
cubic  centimeters  or  grams  of  pure  water,  have  been  raised 
by  the  heat  of  the  reaction.  Calculate  from  this  the  cal- 
ories of  heat  which  would  be  liberated  by  neutralizing 
125  grams  of  oxalic  acid  in  dilute  solution.  Some  heat 
is  of  course  taken  up  by  the  material  of  the  containing 
vessel ;  how  much,  it  would  be  necessary  to  determine,  if 
greater  accuracy  were  demanded. 

At  least  two   determinations  should  be  made   of  this 
heat  of  neutralization. 


CHAPTEE   III 

COMBINING  WEIGHTS-NOTATION-EQUATIONS- 
STOICHIOMETRY— NOMENCLATURE 

No  experiments.  61  to 


CHAPTEE  IV 


EXPERIMENTS  ILLUSTRATING  THE   RELATION  BETWEEN 
VOLUME,  PRESSURE,  AND  TEMPERATURE   OF  GASES 

1.  The  Law  of  Boyle 
Relation  between  Volume  and  Pressure  of  Gases 

66         Specific  problem. — To  investigate  the  relation  between 
the  volume  and  the  pressure  of  a  confined  mass  of  air,  its 
temperature  remaining  constant. 

Use  a  gasometric  tube  of  25  cubic  centi- 
meters in  capacity,  graduated  in  fifths  (the 
inside  must  be  dry),  filled  about  one  third  or 
one  half  with  air,  the  rest  with  mercury,  and 
inserted,  the  open  end  down,  in  a  narrow  cyl- 
inder containing  mercury.  Hold  the  tube, 
using  a  paper  holder  to  avoid  changing  the 
temperature  by  contact  with  the  hand,  in  a 
fixed  position  ;  observe  the  volume  occupied 
by  the  gas,  reading  from  the  top  of  the  mer- 
cury column ;  measure  also,  the  position  be- 
ing unchanged,  the  length  of  the  mercury 
column  from  its  top  to  the  free  surface  of  the 
mercury  in  the  cylinder,  using  a  metric  rule 
or  a  common  one,  according  to  convenience. 
Now  change  the  position  of  the  tube  verti- 
cally, read  the  new  volume,  and  measure  the 
new  length  of  column.  In  this  manner  make  the  observa- 
tions in  five  or  six  different  positions  of  the  tube. 
44 


FIG.  3.— Appa- 
ratus to  show 
Boyle's  law. 


VOLUME,  PRESSURE,  AND  TEMPERATURE  OP  GASES    45 

Calculations. — It  will  be  found  convenient  to  record  the  66/1 
volumes  in  a  vertical  column,  and  the  lengths  in  a  column 
parallel  with  this,  each  corresponding  horizontally  with  its 
proper  volume.  Deduct  the  several  lengths  of  mercury 
column  from  the  length  of  the  mercury  column  in  the 
barometer,  and  the  differences  thus  obtained  measure  the 
relative  pressures  of  the  gas  when  it  occupies  the  corre- 
sponding volumes.  Xow,  looking  for  a  relation  between 
the  numbers  measuring  volume  and  those  measuring  pres- 
sure, multiply  each  volume  by  its  corresponding  pressure 
and  compare  the  products.  (See  Appendix,  15  B.) 

How  comes  it  that  pressure  is  measured  in  linear  units  ?  And  why 
is  the  observed  pressure  obtained  by  subtracting  the  observed  length  of 
column  from  the  barometric  length  ? 

What  is  the  limit  of  accuracy  in  your  measurement  of  volume  ¥  Of 
pressure?  How  much  variation  from  constancy  may  the  products 
show  and  still  prove  constancy  within  the  limits  of  observational  accu- 
racy? What  does  constancy  in  the  products  prove  concerning  the 
factors  ? 

2.  The  Law  of  Charles 
Relation  between  Volume  and  Temperature  of  Gases 

Specific  problem. — To  investigate  the  relation  between  67 
the  volume  and  the  temperature  of  a  confined  mass  of  air, 
its  pressure  remaining  constant. 

Use  an  apparatus  of  the  following  description  :  A  gaso- 
metric  tube  of  25  cubic  centimeters  in  capacity,  graduated 
in  fifths  (the  inside  must  be  dry),  filled  about  one  third  or 
one  half  with  air,  and  the  rest  with  mercury.  This  is  in- 
verted, and  the  open  end  inserted  in  a  shallow  vessel  con- 
taining mercury.  Outside  the  gasometric  tube  is  a  larger 
glass  tube,  serving  as  a  jacket,  which  is  closed  at  the  lower 
end  by  a  stopper,  through  which  pass  centrally  the  gaso- 
metric tube  and,  either  side  of  this,  one  small  tube  to  carry 
steam  and  one  to  drain  off  the  water.  A  thermometer  is 
suspended  beside  the  gasometric  tube  from  a  stopper  which 


ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


loosely  fits  the  upper  end  of  the  jacket.  A  flask  is  con- 
nected so  that  steam  may  be  passed  into  the  jacket  at  will, 

and  the  whole  apparatus  is 
fixed  firmly  in  position. 

When  it  has  stood  long 
enough  to  make  sure  that 
the  inclosed  air  has  the 
temperature  indicated  by 
the  thermometer,  read  the 
volume,  pressure,  and  tem- 
perature. Then  apply  heat 
to  the  flask  containing  wa- 
ter, and  pass  steam  into  the 
jacket  until  the  thermom- 
eter reaches  its  maximum 
and  holds  it  steadily  for 
fifteen  or  twenty  minutes. 
Finally,  read  again  the  vol- 
ume, pressure,  and  temper- 
ature. Calculate  the  aver- 
age increase  in  volume  for 
1°,  on  unit  volume,  at  the 
initial  temperature,  pres- 
sure being  constant.  To  put 
this  result  into  conventional 
form,  so  that  it  shall  be 
comparable  with  the  result 
as  given  in  books,  it  is  only 
necessary  to  assume  the 

same  rate  of  change  between  the  initial  temperature  and  0°, 
that  you  have  observed  between  the  initial  and  final  tem- 
peratures, and  from  this,  to  calculate  the  average  increase 
in  volume  per  degree  on  unit  volume  at  0°.  This  is  called 
the  increment  of  volume,  also  the  coefficient  of  expansion. 

[What  would  be  the  effect  of  moisture  in  the  gasometric 
tube  on  your  experimental  result  ?] 


FIG.  4. — Apparatus  to  show  Charles's 
law.  A,  jacket ;  B,  gasometric 
tube  containing  air  ;  T,  thermom- 
eter ;  8,  rubber  tube  to  convey 
steam  from  the  flask,  F ;  W,  tube 
to  carry  off  water. 


CHAPTEE  Y 

EXPERIMENTS   ILLUSTRATING   THE   RELATION   BETWEEN 

EQUIVALENT  AND  COMBINING  WEIGHTS  AND 

CERTAIN  SPECIFIC  PROPERTIES 

1.  The  Law  of  Gay-Lussac 

Relation  between  Equivalent  and  Combining  Weights  of 
Gases,  Elementary  and  Compound,  and  their  Specific 
Gravities 

Specific  problem. — To  determine  experimentally  the  spe-   71 
cine  gravity  (A)  of  oxygen,  (B)  of  carbon  dioxide,  and  to 
investigate    the    numerical  relation  between   these  values 
and  the  combining  weights  of   the  substances,  assuming 
that  the  formula  of  the  latter  is  C02. 

[What  is  the  specific  gravity  by  definition  ?  (see  No.  7, 
Part  I.)  What  are  these  combining  weights,  numeric- 
ally?] 

Assume  that  the  weight  of  one  liter  of  hydrogen  at  0° 
and  760  millimeters  is  known  to  be  0.0899  of  a  gram.  The 
experimental  problem  then  becomes,  to  determine  the 
weight  of  one  liter  of  the  gas  in  question  at  0°  and  760 
millimeters;  or,  if  preferred,  to  determine  the  weight  of 
any  measured  volume  of  the  gas  at  an  observed  tempera- 
ture and  pressure.  The  most  direct  method  of  solution 
would  be  to  weigh  a  mass  of  the  gas  in  a  vessel  of  meas- 
ured capacity ;  but  the  experimental  difficulties  in  doing 
this  make  it  impracticable  for  beginners.  (Can  you  sug- 
gest some  of  the  difficulties?)  A  less  direct  method  is 
therefore  followed. 

47 


48          ELEMENTARY  PRINCIPLES  OP  CHEMISTRY 


To  determine  the  weight  of  one  liter  of  oxygen : 
71/A         Use  a  large  test-tube  (about  230  millimeters  or  9  inches 
long)  fitted  with  a  rubber  stopper,  carrying  a  glass  and 
rubber  delivery  tube,  like  that  of  the  gas  generator.     The 
test-tube  must  be  thoroughly  dry. 

Weigh  out  roughly  about  5  grams  of  manganese  dioxide 
(symbol  Mn02).  Place  this  in  the  porcelain  crucible  and 
ignite  it  with  the  full  heat  of  the  flame  for  ten  or  fifteen 
minutes  to  insure  complete  dryness. 

Weigh  out  roughly  about  20  grams  of  powdered  potas- 
sium chlorate  (symbol  KC103).  Mix  the  two  substances 
thoroughly  in  a  clean  mortar ;  transfer  to  the  test-tube, 
and  wipe  any  adhering  dust  from  the  upper  part  of  the 
tube.  Insert,  to  lie  just  back  of  the  stopper,  a  loose  plug 
about  15  millimeters  (one  half  inch)  wide,  made  of  a  coiled 
strip  of  asbestos  board  or  of  glass  wool. 

Weigh  carefully,  to  hundredths,  the  tube  and  contents 
thus  prepared. 

Support  the  tube  horizontally  between  two  rings  of  the 
iron  stand,  and  tap  it  gently  so  that  the  powder  shall  lie 
somewhat  spread  out.  Insert  the  stopper  and  connect  with 
the  large  collecting  bottle  in  the  tank. 

Eecall  the  experiment  (No.  41/3  c)  with  hydrogen  under 
Law  4,  Chapter  II,  and  follow  here  the  details  of  manipu- 
lation there  directed  for  the  collection  and  measurement  of 
the  gas  generated. 

Heat  the  mixture  gently  so  as  to  avoid  too  rapid  evolu- 
tion of  gas.  It  is  best  to  apply  heat  to  only  a  small  por- 
tion of  the  mixture  at  a  time,  for,  if  the  whole  mass  be- 
comes heated,  the  evolution  of  gas  will  not  cease  when  the 
flame  is  withdrawn,  and  more  than  the  bottleful  may  be 
generated.  When  nearly  sufficient  .gas  to  fill  the  bottle  has 
been  collected,  withdraw  the  heat,  and  when  bubbles  cease 
to  pass,  remove  the  stopper,  lest  water  be  drawn  into  the 


COMBINING   WEIGHTS  AND  SPECIFIC   PROPERTIES   49 

tube  ;  let  the  tube  cool,  and  carefully  weigh  it.  The  loss  in 
weight  is  taken  as  the  weight  of  the  oxygen  which  has 
passed  out  of  the  tube. 

The  volume  of  this  gas  is  measured  in  the  collecting 
bottle,  as  before  indicated.  It  is  well  to  shake  the  gas  with 
the  water  remaining  in  the  bottle,  and  then  to  reopen  the 
bottle  for  a  second  under  water.  (Why?) 

Calculations, — From  this  weight  and  this  volume  calcu-   71/1 
late  the  weight  of  one  liter  of  oxygen  at  0°  and  760  milli- 
meters, and  from  this  value  calculate  the  specific  gravity 
of  the  gas  and  compare  it  with  its  combining  weight. 

Make  a  second  determination  of  the  same.  The  origi- 
nal charge  will  be  more  than  sufficient  to  generate  two 
bottlefuls. 

Secondary  observation. — After  the  second  determination,   71/2 
collect  some  of  the  gas  in  a  small  bottle  and  test  it  with  a 
lighted  match.     (See  Appendix,  19,  I  and  IV.) 

EXPLANATORY  NOTE — The  potassium  chlorate,  symbol  KC103,  by 
heating  loses  its  oxygen  and  becomes  potassium  chloride,  symbol  KC1. 
The  temperature  at  which  this  decomposition  takes  place  is  lowered  by 
the  presence  of  the  manganese  dioxide,  hence  its  use. 

B.   First  Step 

To  determine  the  weight  of  the  carbon  dioxide  gener- 
ated from  a  weighed  quantity  of  calcium  carbonate  by  the 
action  of  an  acid  : 

Weigh  out  with  care  5.00  grams  of  this  substance  in  pow-  81/1 
der.     Transfer  it  without  loss  to  a  filter  paper,  wiping  off 
any  dust  adhering  to  the  glass  crystal  with  a  small  piece  of 
paper.     Wrap  the  whole  in  a  small  package,  and  put  it  in 
a  beaker.     Weigh  this  beaker  with  its  contents. 

In  a  second  beaker  put  about  20  grams  (15  c.  c.)  of  nitric 
acid  and  a  glass  rod,  and  weigh  this  beaker  with  its  contents. 
Cautiously  pour  acid  from  the  second  beaker  into  the  first,  a 
little  at  a  time,  until  there  is  no  further  action.  Then  weigh 


50          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

again  each  beaker  and  its  contents.  The  loss  of  weight  in 
the  system  is  taken  as  the  weight  of  carbon  dioxide  gener- 
ated. Make  at  least  two  determinations  of  this  quantity. 

B.    Second  Step 

To  determine  the  volume  of  the  gas  generated  by  the 
action  of  d,n  acid  on  a  weighed  quantity  of  calcium  car- 
bonate : 

81/2  Weigh  out  10.00  grams  of  the  calcium  carbonate,  wrap  in 
a  paper  as  in  No.  81/l5  and  transfer  without  loss  to  the  gas 
generator.  Now,  carbon  dioxide,  being  soluble  in  water, 
can  not  be  collected  over  water  without  loss.  The  difficulty 
is  avoided  by  using  an  intermediate  bottle,  holding  about 
four  times  as  much  as  the  collecting  bottle.  It  is  provided 
with  a  two-holed  stopper,  through  one  hole  of  which  passes 
a  bent  glass  tube,  terminating  close  to  the  bottom  of  the 
bottle  ;  through  the  second  hole  passes  a  tube  terminating 
just  below  the  stopper,  and  to  the  outer  end  of  this  is 
attached  a  rubber  tube  carrying  the  delivery  tube.  The 
delivery  tube  of  the  generator  is  now  connected  with  the 
first  tube  of  the  large  bottle,  and  the  delivery  tube  of  the 
latter  is  inserted  in  the  mouth  of  the  collecting  bottle. 
The  gas  from  the  generator  will  thus  be  passed  to  the  bot- 
tom of  the  large  bottle  and,  being  considerably  heavier  than 
air,  will  lie  there  some  little  time,  while  an  equal  volume  of 
air  will  pass  out  from  the  top  and  may  be  collected  arid 
measured,  as  in  the  hydrogen  experiment.  After  the  con- 
nections are  made  the  apparatus  should  be  tested  for  leak- 
age (see  Exp.  41/3b). 

Pour  about  40  grams  (30  c.  c.)  of  nitric  acid,  a  little  at  a 
time,  through  the  thistle-tube  until  the  reaction  ceases. 
Note  the  volume  of  the  acid  used  (why?),  the  temperature  of 
the  water  in  the  tank,  that  of  the  room,  and  the  height  of 
the  barometer.  Make  thus  at  least  two  determinations  of 
the  volume  of  gas  generated, 


COMBINING  WEIGHTS  AND  SPECIFIC  PROPERTIES     51 

Calculations. — From    these    observations    calculate    first  81/3 
the  weight  of  one  liter  of  the  gas  at  0°  and  760  millime- 
ters, then  the  specific  gravity  referred  to  hydrogen,  and 
finally  the  ratio  of  the  specific  gravity  to  the  combining 
weight. 

NOTE. — The   intermediate    bottle,  after   once   serving,  81/4 
before  being  again  used,  must  be  cleaned  of  its  gas.     This 
may  be  done  by  blowing  it  out  with  a  pair  of  bellows,  the 
nozzle  of  which,  extended  by  a  rubber  tube,  reaches  to  the 
bottom  of  the  bottle. 

EXPLANATORY  NOTE. — In  this  reaction  the  factors  are  calcium  car-    81/5 
bonate  (a  salt)  and  nitric  acid ;  the  products  are  calcium  nitrate  (a 
soluble  salt),  water,  and  carbon  dioxide,  the  latter  appearing  as  a  gas. 
This  may  be  expressed  by  equation,  thus  : 

CaC03  4-  2HN03  =  Ca(NOs)3  +  H20  -f  C02 
calc.  nitric  calc.  water,  carbon 

carb.  acid.  nitrate.  dioxide. 

Recall  the  similar  reaction  in  the  experiment  under  Law  1,  Chapter  II 
(No.  36). 


2.  The  Law  of  Dulong  and  Petit 

Relation  between  Equivalent  and  Combining  Weights  of 
Elementary  Solids  and  their  Specific  Heats 

Definition  of  specific  heat.— The  specific  heat  of  a  sub-  95 
stance  is  the  quantity  of  heat  required  to  raise  in  tempera- 
ture 1  gram  of  the  substance  1°,  divided  by  the  quantity  of 
heat  required  to  raise  1  gram  of  water  1°. 

It  is  necessary  to  discriminate  carefully  between  quan- 
tity of  heat  and  temperature.  The  unit  of  quantity  (see 
No.  50/i)  is  called  the  gram-calorie,  and  is  the  quantity  of 
heat  required  to  raise  one  gram  of  water  one  degree  (strictly 
from  0°  to  1°,  practically  from  19°  to  20°  or  thereabouts). 
Therefore  specific  heat  may  better  be  defined  as  the  quan- 
tity of  heat,  measured  in  gram-calories,  required  to  raise 
one  gram  of  the  substance  one.  degree. 


52          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

95/1  Specific  problem. — To  determine  experimentally  the  spe- 
cific heat,  and  to  investigate  the  numerical  relation  be- 
tween this  value  and  the  combining  weight  in  the  case  (A) 
of  lead,  (B)  of  zinc,  (C)  of  tin.* 


95/2  Specific  heat  of  lead. — Weigh  out  carefully  100.0  grams 
of  lead  (shot),  transfer  it  to  a  large  dry  test-tube,  set  the 
tube  and  contents  in  water  contained  in  a  suitable  vessel, 
and  boil  the  water.  The  lead  should  be  immersed  below 
the  surface  of  the  water. 

Weigh  out  carefully  in  a  beaker  50.0  grams  of  water 
which  has  the  temperature  of  the  room;  test  with  the 
thermometer  to  see  that  the  temperature  does  not  change 
in  an  interval  of  five  minutes.  Put  the  thermometer,  first 
drying  it,  in  the  lead,  and  see  that  it  reaches  a  maximum 
which  it  holds  for  at  least  five  minutes.  Eecord  this  tem- 
perature. Then  put  the  thermometer  back  in  the  water, 
stir,  read  the  temperature  carefully,  and  record  it. 

Now,  as  quickly  as  possible,  take  the  test-tube  from  the 
water,  pour  the  warm  lead  into  the  water  which  the  beaker 
contains,  stir  gently  with  the  thermometer,  quickly  read 
the  maximum  temperature  and  record  it. 

The  observations  therefore  are :  The  weight  of  the  water 
and  its  temperature  just  before  mixing ;  the  weight  of  the 
lead  and  its  temperature  just  before  mixing ;  the  tempera- 
ture of  the  resultant  mixture. 

95/3        Calculations.— Let 

x  =  the  quantity  of  heat  required  to  raise  1  gram  of  lead  1°  ; 
y  =  the  quantity  of  heat  required  to  raise  1  gram  of  water  1° ; 

t  =  the  degrees  of  temperature  lost  by  the  lead ; 

t'=  the  degrees  of  temperature  gained  by  the  water. 

*  One  of  these  three  determinations  may  be  thought  sufficient,  or 
perhaps  all  may  be  omitted  if  the  student  has  already  made  similar 
ones  in  physics. 


COMBINING  WEIGHTS  AND  SPECIFIC  PROPERTIES     53 

It  follows  that 

100  X  t  X  x  =  the   quantity  of  heat  lost  by  100 

grams  of  lead  in  cooling  t°. 

50  X  t'  X  y  =  the  quantity  of  heat  gained  by  50 
grams  of  water  in  warming  t'  °. 

If  now  the  experimental  conditions  are  made  such  that 
the  lead  shall  lose  no  heat  save  what  goes  to  the  water,  and 
the  water  gain  no  heat  save  what  comes  from  the  lead,  then 
these  two  quantities  of  heat  must  be  equal.  Equating  the 
two  expressions  gives 

100  X  t  X  x  =  50  X  t'  X  y. 
From  which  is  obtained 

-  —  —— =  Specific  heat  by  definition. 

The  experimental  conditions  called  for  to  justify  this 
equation  can  be  but  crudely  realized  by  the  directions  here 
given,  but  sufficiently  to  give  a  good  illustration  of  method. 
Calculate  the  quantity  of  heat  required  to  raise  205  grams 
of  lead  1°. 

B 

Specific  heat  of  zinc. — Weigh  out  carefully  50.0  grams  of  95/4 
granulated  zinc,  and  50.0  grams  of  water.     The  procedure 
and  calculations  are  the  same  as  in  the  case  of  lead.     Cal- 
culate the  quantity  of  heat  required  to  raise  65  grams  of 
zinc  1°. 

C 

Specific  heat  of  tin. — Use  50.0  grams  of  tin  in  coarse  95/5 
powder,  and  50.0  grams  of  water,  and  proceed  as  in  B. 
Calculate  the  quantity  of  heat  required  to  raise  118  grams 
of  tin  1°. 

NOTE. — Save  the  material  used  in  these  experiments,  so  that  it  may 
be  dried  and  be  ready  for  use  again. 
21 


54          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

3.  The  Law  of  Mitscherlich 

Relation  betiveen  Composition,  and  hence  Combining  Weight, 
and  Specific,  i.  e.,  Crystalline  Form 

107         No  experiments. 

4.  The  Law  of  Baoult  (I) 

Relation  between  Combining  Weights  of  Solutes  and  Specific 
Depressions  of  the  Freezing  Point  in  Specified  Solvent 
(See  Part  I,  Nos.  21  and  23/0 

111  Specific  problem. — I.  To  investigate  experimentally  the 
relation  between  the  depression  of  the  freezing  point  and 
the  quantity  of  the  solute  (A)  when  the  solute  is  camphor 
and  the  solvent  paraffin ;  and  (B)  when  the  solute  is 
naphthalene  and  the  solvent  paraffin. 

II.  To  investigate  the  numerical  relation  between  the 
specific  depression  (i.  e.,  depression  for  1  gram  of  solute 
in  100  grams  of  solvent)  of  camphor  in  paraffin,  and  of 
naphthalene  in  paraffin,  and  the  combining  weights  of  the 
solutes. 

A 

111/1  (1)  Weigh  out  carefully  10.00  grams  of  paraffin  and  0.80 
of  a  gram  of  camphor.  Melt  the  paraffin  in  an  evaporating 
dish  on  the  water-bath,  then  add  the  camphor  and  let  it 
dissolve,  stirring  well.  Pour  a  suitable  portion  of  the  solu- 
tion into  a  clean,  dry  test-tube.  Let  the  liquid  be  about 
one  inch  deep.  In  another  tube  put  some  paraffin.  Have 
a  stirring-rod  in  each  tube,  and  attach  the  tubes  by  rubber 
bands  to  a  thermometer.  Suspend  the  tubes  in  a  beaker 
containing  water,  so  that  they  are  suitably  immersed,  and 
apply  heat  until  the  mixture  melts.  Allow  to  cool  very 
slowly,  keeping  the  mixtures  and  the  water  well  stirred,  and 
observe  the  freezing  points.  Repeat  several  times  for  con- 
stant results.  It  will  save  time  to  prepare  the  solution 


COMBINING  WEIGHTS  AND  SPECIFIC   PROPERTIES     55 

called  for  in  Exp.  lll/2,  and  to  attach  the  three  tubes  at 
one  time  to  the  thermometer. 

(2)  Make  a  mixture  of  10.00  grams  of  paraffin  and  1.20   111/2 
grams  of  camphor,  as  in  (1),  and  in  a  similar  manner  deter- 
mine  its   freezing   point.      Are   the   depressions   approxi- 
mately proportional  to  the  quantities  of  the  solute  in  a 
constant  quantity  of  the  solvent  ? 

Calculate  the  specific  depressions — i.  e.,  depressions  for 
1  gram  of  solute  in  100  grams  of  solvent — and  take  their 
average. 

B 

(3)  Make  a  mixture  of  10.00  grams  of  paraffin  and  0.60   111/3 
of  a  gram  of  naphthalene,  as  in  A  ;  (4)  also  of  10.00  grams   111/4 
of  paraffin  and  1.20  grams  of  naphthalene.     Observe  the 
freezing  points,  and  make  the  calculations  as  before. 

II.  Multiply  the   specific   depressions   of  camphor    in   111/5 
paraffin  by  the  combining  weight  of  camphor  (C10H160  = 
151),  and  the  specific  depression  of  naphthalene  by  the 
combining  weight  of  naphthalene  (C10H8  =  127),  and  com- 
pare the  products.     Are  they  approximately  constant  ? 

NOTE. — It  will  be  realized  that  the  probable  error  of  reading  on  the  111/6 
ordinary  thermometer  is  so  large  a  fraction  of  the  depression  itself, 
that  the  results  can  not  be  quantitatively  very  satisfactory.  A  ther- 
mometer reading  at  least  to  hundredths  would  be  needed  for  good 
results.  Calculate  the  variation  in  the  product  made  by  the  variation 
of  one  quarter  of  a  degree  in  the  depression. 

NOTE. — The  tubes  may  be  cleaned  by  immersing  in  boiling  water,    111/7 
and  the  dishes  by  wiping  with  filter  paper  while  still  warm. 

5.  The  Law  of  Baoult  (II) 

Relation  between  Combining  Weights  of  Solutes  and  Specific 
Elevations  of  Boiling  Temperature  in  Specified  Solvent 
(See  Part  1,'^os.  21  and  24/4) 

Specific  problem.— I.  To  investigate  experimentally  the  127 
relation  between  the  elevation  of  the  boiling  temperature 


56          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

and  the  quantity  of  the  solute  (A)  when  the  solute  is 
sodium  acetate  and  the  solvent  water,  and  (B)  when  the 
solute  is  potassium  tartrate  and  the  solvent  water. 

II.  To  investigate  the  numerical  relation  between  the 
specific  elevation  of  boiling  temperature — i.  e.,  elevation 
for  1  gram  of  solute  in  100  grams  of  solvent — by  sodium 
acetate  in  water,  and  by  potassium  tartrate  in  water,  and 
the  combining  weights  of  the  solutes. 

A 

127/1  (1)  Use  a  small  distilling  flask,  as  in  the  observation  of 
boiling  point  (see  Appendix,  17).  Put  in  it  a  suitable 
quantity  of  water  and  some  bits  of  pumice  (why  the  lat- 
ter ?  See  No.  24/2,  Part  I),  boil,  and  observe  carefully  the 
temperature  of  the  boiling  water.  Repeat  all  readings  for 
constant  results. 

127/2  (2)  Drain  the  water  thoroughly  from  the  flask,  and  put 
in  its  place  a  solution  of  100.0  grams  (or  100  cubi$  centi- 
meters) of  water  and  15.00  grams  of  sodium  acetate  with 
clean  pumice.  Again  observe  the  temperature  of  the  boil- 
ing solution. 

127/3  (3)  In  a  similar  manner  observe  the  boiling  tempera- 
ture of  a  solution  containing  100.0  grams  (or  100  cubic 
centimeters)  of  water  and  30.00  grams  of  sodium  acetate. 

Are  the  elevations  approximately  proportional  to  the 
quantities  of  the  solute  in  'a  constant  quantity  of  the  sol- 
vent ?  Calculate  the  specific  elevations,  and  take  their 
average. 

B 

127/4  (4)  Observe  the  boiling  temperature  of  a  solution  of 
100.0  grams  (or  100 » cubic  centimeters)  of  water  and  20.00 

127/5  grams  of  potassium  tartrate;  (5)  also  of  100.0  grams  (or 
100  cubic  centimeters)  of  water  and  40.00  grams  of  potas- 
sium tartrate.  Make  the  same  calculations  as  before. 


COMBINING  WEIGHTS  AND  SPECIFIC  PROPERTIES     57 

II.  Multiply  the  specific  elevation  of  sodium  acetate   127/6 
(NaC2H302)  in  water  by  the  combining  weight  of  the  same, 
and  the  specific  elevation  of  potassium  tartrate  (K2C4H406) 
by  its  combining  weight,  and  compare  the  products.     Are 
they  approximately  constant  ? 

The  same  remark  as  to  accuracy  of  observation  applies 
here  as  under  the  preceding  law.  Care  should  be  taken 
that  the  bulb  of  the  thermometer  is  completely  immersed 
in  the  liquid. 

NOTE. — The  solutions  may  be  saved  in  order  to  recover  the  salts  by 
crystallization. 

Alternative  experiment— Instead  of  the  solutions  indi-  127/7 
cated  in  the  preceding  experiment,  may  be  used  the  follow- 
ing :  A  15.40  per  cent  and  a  30.80  per  cent  solution  of  potas- 
sium chloride  (KC1),  and  an  11.00  per  cent  and  a  22.00  per 
cent  solution  of  ammonium  chloride  (NH4C1). 


CHAPTER  VI 

EXPERIMENTS  ILLUSTRATING  THE  METHOD  OP  DETER- 
MINING EQUIVALENT  AND  COMBINING  WEIGHTS 
OF  ELEMENTS     AND  FORMULAS  OF 
COMPOUNDS 

1.  Determination  of  the  Equivalent  Weight  of  an  Element 

144  Specific  problem. — To  determine  experimentally  the  mass 
of  tin  which  combines  with  7.94  grams  of  oxygen.  (Tin 
does  not  combine  with  hydrogen.) 

14-4/1  EXPLANATORY  NOTE. — It  is  not  practicable  to  cause  a  weighed  quan- 
tity of  tin  to  combine  with  oxygen  of  the  air,  and  to  weigh  the  oxide 
obtained  ;  but  by  the  action  of  nitric  acid,  the  oxidizing  power  of 
which  has  already  been  noted  [in  what  connection  f],  an  oxide  of  tin  is 
produced  which  does  not  volatilize,  does  not  combine  with  nitric  acid, 
and  does  combine  with  water,  forming  a  compound,  however,  from 
which  the  water  is  expelled  by  prolonged  heating,  leaving  simply  the 
oxide.  The  excess  of  nitric  acid  is  also  volatilized  by  heat. 

144  Weigh  very  carefully  to  hundredths  of  a  gram  a  small  evap- 
orating dish,  clean  and  dry,  together  with  a  short  glass  rod. 
Weigh  out  carefully  5.00  grams  of  pure  tin  foil.  Put  a 
portion  of  this  in  small  pieces  in  the  evaporating  dish,  and 
just  moisten  with  nitric  acid.  When  the  action  is  nearly 
over,  put  in  more  tin,  and  then  moisten  again  with  acid. 
Continue  this  until  all  the  tin  is  used,  with  the  minimum 
of  acid  that  will  suffice. 

Describe  what  takes  place.  What  is  the  brown  gas  produced? 
Have  care  not  to  inhale  it ;  it  is  well  to  use  the  hood.  Also  bear  in 
mind  the  extreme  corrosiveness  of  nitric  acid.  Use  the  rod  to  pour  by, 
leaving  it  in  the  dish.  Keep  the  outside  of  the  beaker  clean.  Have  a 
wet  sponge  at  hand. 
58 


DETERMINING  EQUIVALENT  WEIGHTS  59 

Heat  the  dish  and  contents  on  the  water-bath  until  the 
liquid  has  entirely  volatilized,  transfer  to  the  iron  ring  of 
the  stand,  apply  the  direct  flame,  gently  at  first  passing  it 
back  and  forth,  then  give  it  the  full  heat  of  the  burner, 
continuing  for  some  time  after  the  fumes  have  ceased  to 
appear.  The  powder  should  be  slightly  brown  when  hot, 
and  yellowish  when  cool. 

Let  the  dish  become  thoroughly  cool,  and  weigh  it  with 
its  contents  to  hundredths  of  a  gram.  To  insure  the  com- 
pleteness of  the  operation,  ignite  again  for  fifteen  or 
twenty  minutes,  let  cool,  and  weigh  again. 

Assuming  that  you  have  in  the  dish  a  compound  con-  144/2 
taining  only  tin  and  oxygen,  calculate  the  weight  of  oxy- 
gen which  has  combined  with  the  5  grams  of  tin,  and  from 
this  the  weight  of  tin  which  combines  with  7.94  grams  of 
oxygen.     Make  at  least  two  complete  determinations. 

2.  Determination  of  the  Combining  Weight  of  an  Element 

Under  the  law  of  Dulong  and  Petit  choose  what  mul-  150 
tiple  of  the  equivalent  weight  determined  in  No.  144/2  shall 
be  taken  as  the  combining  weight  of  tin.     The  specific 
heat  of  tin  is  0.056.     (See  Nos.  101  and  105,  Part  I.) 

It  will  be  realized  that  the  utmost  care  must  be  taken   150/1 
in  the  manipulation,  since  the  weighings  must  be  to  hun- 
dredths of  a  gram,  and  the  variation  in  the  quantity  of 
oxygen  for  5  grams  of  tin  should  not  be  more  than  one  or 
two  hundredths  of  a  gram. 

Having  determined  the  combining  weight  of  tin,  deduce  the  for-    150/2 
mula  for  the  oxide.    Try  to  write  the  equation  for  the  reaction  between 
tin  (symbol,  Sn)  and  nitric  acid,  HNOS.    What  is  the  percentage  of  tin 
and  of  oxygen  in  tin  oxide  ? 

3.  Determination  of  the  Formula  of  a  Compound 

Specific  problem. — To  determine  the  percentage  of  the  154 
proximate  constituents,  carbon  dioxide,  C02,  and  sodium 


60          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

oxide,  Ka.,0,  in  the  compound,  sodium  carbonate,  and  from 
these  to  deduce  the  formula  of  the  compound. 
154/a  (a)  To  determine  the  percentage  of  carbon  dioxide : 
Take  a  sufficient  quantity  of  the  sodium  carbonate  for  all 
the  following  experiments,  heat  in  the  larger  evaporating 
dish  over  the  flame,  gently  and  not  too  hot.  This  is  simply 
to  secure  the  dryness  of  the  sample. 

Weigh  out  carefully  5.00  grams  of  the  dry  sample,  and 
follow  the  procedure  given  for  determining  the  weight  of 
carbon  dioxide  in  calcium  carbonate  (see  Exp.  81/j),  using 
hydrochloric  instead  of  nitric  acid.  Make  at  least  two 
determinations. 

Calculate  the  result  as  grams  of  carbon  dioxide  in  100 
grams  of  the  sample. 

Secondary  observation. — Filter  and  crystallize  the  salt  which  is  left 
in  solution.  What  substance  is  it  ? 

(I)  To  determine  the  percentage  of  sodium  oxide : 

154/1  EXPLANATORY  NOTE. — Since  it  is  not  practicable  to  separate  this 
constituent  from  the  compound,  and  weigh  it  by  itself,  it  is  necessary 
to  convert  it  quantitatively  into  some  substance  which  it  is  practicable 
to  separate  and  weigh,  and  the  composition  of  which  is  known.  For 
this  purpose  the  carbonate  is  converted  into  sodium  nitrate  by  the 
action  of  nitric  acid,  the  carbon  dioxide  escapes,  and  the  water  and 
excess  of  nitric  acid  are  volatilized.  Sodium  nitrate  is  not  volatile,  and 
is  not  decomposed  by  heating  short  of  fusion.  Its  composition  is  given 
by  the  formula  Na2N206,  or,  as  usually  expressed,  NaNOs.  [What  per- 
centage of  Na20  does  this  formula  show  ?] 

154/b  Weigh  out  carefully  5.00  grams  of  the  dry  sample  of 
sodium  carbonate  in  a  small  evaporating  dish,  the  weight 
of  which  has  been  determined  to  hundredths  of  a  gram. 
Neutralize  this  with  nitric  acid,  using  a  very  slight  excess, 
and  having  care  not  to  lose  by  effervescence.  Evaporate 
on  the  water-bath  until  the  liquid  has  disappeared,  and 
then,  passing  the  burner  back  and  forth,  heat  gently  until 
the  substance  just  begins  to  melt.  Let  cool,  and  weigh. 
The  substance  obtained  is  sodium  nitrate.  Make  thus  at 


DETERMINING  EQUIVALENT  WEIGHTS  61 

least  two  determinations  of  the  weight  of  this  substance 
obtained  from  5  grams  of  the  carbonate. 

Knowing  the  percentage  of  sodium  oxide  in  sodium 
nitrate,  calculate  the  weight  of  sodium  oxide  contained  in 
the  weight  of  the  nitrate  obtained,  and  reckon  this  result 
as  grams  of  the  oxide  in  100  grams  of  the  carbonate. 

Secondary  observation. — Redissolve  and  crystallize  the  sodium  ni- 
trate. 

(c)  To  deduce  the  formula  : 

Since  the  proximate  constituents  are  carbon  dioxide,  155 
C02,  and  sodium  oxide,  Na20,  the  formula  must  be  (Na20)a; 
(C02)y,  the  coefficients,  x  and  «/,  to  be  deduced  from  the 
percentages  experimentally  obtained.  Hence  divide  the 
percentage  of  each  constituent  by  the  combining  weight  of 
the  same,  and  the  quotients  give  the  ratio  of  the  coefficients, 
x  and  y.  Now  these  quotients  are  not  necessarily  whole 
numbers,  but  the  peculiarity  of  chemical  phenomena  is 
that  they  stand  in  the  ratio  of  whole  numbers,  usually  quite 
small.  Hence  inspection  or  division  by  the  smallest  will 
suffice  to  show  the  smallest  whole  numbers  that  have  the 
ratio  of  the  quotients.  In  this  specific  problem  the  ap- 
proach of  the  quotients  to  equality  measures  the  accuracy 
of  the  experimental  work.  The  simplest  values,  therefore, 
for  x  and  y  are  1  and  1,  and,  in  the  properties  of  this  sub- 
stance, no  reason  is  found  for  using  any  multiples  of  these 
values.  The  accepted  formula  is  therefore  Na2OC02,  or, 
as  it  may  also  be  written,  ]STa2C03. 

[Write  the  equation  for  the  reaction  between  sodium 
carbonate  and  nitric  acid.] 


CHAPTER  VII 

THE  ATOMIC  THEORY 


157  to         NO  experiments. 
187 


CHAPTER  VIII 

RELATION  BETWEEN  THE  PROPERTIES  OF  THE  ELEMENTS 
IN  GENERAL  AND  THEIR  COMBINING  WEIGHTS 

Experimental  Study  of  the  Properties  of  the  First  Twenty- 
five  Elements  (in  the  Order  of  their  Combining  Weights] 
and  Some  of  their  Compounds 

So  far  as  practicable,  each  element  in  turn  will  be  presented  in  its 
free  condition  for  descriptive  study  :  first  as  to  its  physical  properties, 
those  which  appear  on  inspection,  and  others ;  second,  as  to  its  chemical 
properties.  Then  will  follow  the  study  of  some  of  its  most  important 
compounds.  It  is  judged  unnecessary  to  give  detailed  directions  for 
manipulation  in  all  experiments,  as  by  this  time  the  student  should 
have  had  sufficient  experience  in  the  laboratory  to  give  him  some  judg- 
ment of  his  own  as  to  how  to  do  things.  Some  of  the  manipulations, 
too,  are  repeated  many  times. 

1.  HYDROGEN 

Symbol  H.— Comb.  wt.  1 

202  Preparation.— See  Exps.  17/i  and  41/4  and  Appendix,  19, 
I.  Use  the  small  collecting  bottles  or  test-tubes.  Use  iron 
(nails)  or  zinc  and  hydrochloric  or  dilute  sulphuric  acid. 

NOTE. — Hydrogen  with,  air  makes  a  mixture  which  may 
explode  dangerously  on  ignition.      Therefore  the  greatest 
62 


DESCRIPTION   OP  ELEMENTS  AND  COMPOUNDS      03 

caution  must  always  ~be  taken  to  avoid  accident  from  unex- 
pected ignition  by  contact  with  flame. 

Physical  Properties 

Observe  as  to  color,  odor  (any  odor  is  due  to  impurity).  203 
As  to  weight  compared  with  air. — A  crude  test :  Fill  a  test- 
tube  with  hydrogen  over  water,  close  with  the  thumb,  hold 
its  mouth  downward  directly  over  and  close  to  the  mouth 
of  a  second  tube,  then  remove  the  thumb  quickly,  bringing 
the  two  ends  together,  reverse  the  position  of  the  tubes, 
separate  them,  closing  the  second,  now  the  upper  one,  with 
the  thumb,  and  test  at  the  flame  for  the  presence  of  hydro- 
gen in  both  tubes. 

As  to  solubility  in  water.— A  crude  test:  Collect  in  a  204 
test-tube,  leaving  a  little  water;   close  tightly  with  the 
thumb,  shake,  open  under  water,  close,  and  shake  again. 
Eepeat  this  several  times,  and  note  if  the  volume  of  water 
in  the  tube  increases  and  the  gas  decreases. 

As  to  relative  divisibility.— Use  a  dry  glass  tube,  closed  203/1 
at  one  end  with  a  porous  plug  of  plaster  of  Paris,  and  open 
at  the  other.  Close  temporarily  the  plugged  end  with  the 
thumb  or  a  cork,  and  fill  the  tube  thoroughly  by  dry  dis- 
placement— i.  e.,  hold  the  tube  open  end  downward,  thrust 
the  delivery  tube  at  first  well  up  to  the  top,  then  slowly 
withdraw  it  (compare  Appendix,  19,  VI).  When  the  tube 
is  full,  immerse  the  lower,  open  end  in  water,  uncover  the 
porous  plug,  and  allow  to  stand  for  some  time.  What 
takes  place  ?  Can  you  explain  the  phenomenon  ? 

A  modification  of  the  preceding  experiment,  suitable  to  be  performed  203/2 
by  the  teacher  before  the  class :  Use  a  porous  battery  jar,  closed  by  a  cork 
or  a  plaster  plug  through  which  passes  a  glass  tube  of  convenient  length. 
Support  this  so  that  the  lower  open  end  of  the  tube  is  immersed  in  a  col- 
ored liquid  (e.  g.,  water,  colored  by  potassium  permanganate).  Slowly 
lower  over  the  porous  jar  a  glass  bell  jar  filled  with  hydrogen.  When 
the  gas  ceases  to  bubble  from  the  end  of  the  tube,  remove  the  bell  jar. 
The  same  may  be  tried  with  illuminating  gas  in  place  of  hydrogen. 


64          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

205  Occlusion. — Hold  a  piece  of  platinum  sponge  (i.  e.,  finely  divided 
platinum  deposited  on  the  surface  of  asbestos  fiber),  thoroughly  dried, 
in  the  stream  of  hydrogen  issuing  from  the  delivery  tube,  but  only 
when  the  gas  is  sufficiently  pure  to  be  ignited  with  safety. 

[This  experiment,  like  the  preceding  one,  may  best  be  performed 
by  the  teacher.] 

Chemical  Properties 

Test  as  to  the  action  of  hydrogen  on  wet  litmus  paper. 

207  Test  as  to  combustibility. — With  suitable  precaution,  the 
gas  issuing  from  the  delivery  tube  may  be  ignited  as  a  jet, 
but,  owing  to  the  danger  of  explosion,  this  should  not  be 
tried  until  the  action  has  continued  long  enough  to  expel 
the  air  from  the  generator.    It  is  best  always  to  test  a  small 
sample  of  the  gas  thus :  Collect  in  a  test-tube  over  water, 
close  with  the  thumb,  bring  it  to  the  flame,  mouth  down- 
ward, remove  the  thumb,  ignite  the  gas,  and  slowly  invert 
the  tube.     The  gas  should  burn  quietly  in  the  tube.     If  it 
burns  quickly  with  a  slight  report,  it  is  not  safe  to  ignite 
at  the  generator. 

207/1  Make  it  a  rule  always  to  wrap  several  folds  of  the  towel 
over  and  around  the  generator  before  igniting  the  gas,  no 
matter  hoiv  confident  you  may  be  of  its  purity.  Serious  ac- 
cident may  follow  neglect  of  this  precaution. 

Observe  the  character  of  the  hydrogen  flame  ;  hold  a 
dry  glass  plate  or  beaker  over  the  flame.  What  is  the  pro- 
duct of  combustion  ? 

208  Nascent  state.— Use  four  test-tubes,  fill  about  two  thirds 
full  with  water,  and  color  each  portion  slightly  with  a  few 
drops  of  potassium  permanganate  solution.     Into  the  first 
put  a  few  fragments  of  zinc  and  a  few  drops  of  sulphuric 
acid,  and  let  the  action  continue  for  some  minutes.     What 
is  the  result  ?    What»substance  is  it  which  causes  the  color 
to  disappear?    To  answer  this,. place  in  the  second  tube 
some  zinc,  in  the  third  some   sulphuric  acid,  and  into 
the  fourth  let  the  hydrogen  from  the  generator  slowly 
bubble,  preferably  using  zinc  as  the  metal. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS      65 

EXPLANATORY  NOTE. — The  permanganate  loses  its  color  in  conse-  208/1 
quence  of  losing  some  of  its  oxygen.  The  oxygen  is  taken  from  it  by 
the  hydrogen,  but  only  at  the  moment  of  its  liberation  from  the  acid, 
when  it  is  said  to  be  in  the  nascent  state.  The  experiment  may  not  be 
entirely  satisfactory,  for  the  reason  that  the  impurity  which  is  usually 
carried  by  the  hydrogen  from  the  generator,  and  which  comes  from  the 
metal,  and  imparts  the  odor  to  the  gas,  tends  to  remove  oxygen  from 
the  permanganate.  Observe  as  to  the  odor  of  the  gas  which  has  bub- 
bled through  the  colored  liquid. 

To  explain  the  phenomenon  of  the  nascent  state  it  has  been  sug-    208/2 
gested  that  the  substance  in  the  atomic  condition  may  show  an  activity 
which  is  wholly  or  partly  lost  after  the  atoms  have  come  together  into 
molecules. 

Another  method  of  generating  hydrogen.— Use  a  few  frag-  202/3 
ments  of  zinc  in  a  test-tube  with  a  dilute  solution  of  sodium 
hydroxide.     The  reaction  is  facilitated  by  a  piece  of  iron 
(a  nail)  in  contact  with  the  zinc. 

2.    LITHIUM 

Li.-6.97 

No   experiments,   unless    to    show   a   sample  of   some  210 
salt  of  lithium — e.  g.,  the  chloride — and  the  color  it  im- 
parts to  the  flame. 

3.   GLUCINUM  or  BERYLLIUM 

Gl.  or  Be.— 9.0 

No  experiments.  216 

4.   BORON 

B.— 10.86 

Boron  is  difficult  of  preparation,  so  it  is  impracticable  to  show  it. 
It  forms  an  oxide  whose  symbol  is  B203,  and  which  combines  with 
water,  forming  boric  acid.  The  sodium  salt  of  this  is  the  familiar  com- 
mercial substance,  borax. 

Borax    and   boric    acid    crystallized.— Saturate   about   a  225 
beakerful  of  water  with  borax.     Filter,  if  not   clear,  and 


66          ELEMENTARY  PRINCIPLES  OP  CHEMISTRY 

set  aside  about  one  half  of  this  to  crystallize.  To  the  re- 
mainder add  about  one  half  its  volume  of  hydrochloric  acid, 
and  set  this  aside  to  crystallize.  Observe  the  different  ap- 
pearance of  the  two  substances  when  crystallized. 

Kinse  a  sample  of  each  substance  quickly  with  a  very 
little  cold  water,  and  dry  it  on  filter  paper.  Observe  the 
reactions  on  litmus  paper. 

226  Flame  coloration. — Put  a  very  small  quantity  of  borax  in 
an  evaporating  dish,  add  a  few  drops  of  alcohol,  ignite  the 
alcohol,  and  observe  the  color  of  the  flame,  while  stirring 
the  mixture.  Extinguish  the  flame,  add  a  few  drops  of 
dilute  sulphuric  acid,  reignite  the  alcohol,  and  again  ob- 
serve the  flame  color.  This  test  is  often  used  to  recog- 
nize boric  acid  and  its  compounds. 

228  The  borax  bead. — Melted  borax  has  the  property  of  dis- 
solving many  metallic  oxides,  and  these  often  impart  charac- 
teristic colors  to  the  substance.  This  test  is  very  useful  in 
qualitative  analysis.  To  make  a  borax  bead,  use  a  piece  of 
platinum  wire,  about  75  millimeters  (3  inches)  long,  one 
end  of  which  is  fused  into  a  piece  of  glass  tubing  for  a 
handle.  Bend  the  free  end  of  the  wire  around  the  sharp- 
ened end  of  a  lead  pencil,  so  as  to  make  a  small  loop.  Heat 
this  red  hot,  touch  it  to  some  powdered  borax,  and  heat  the 
borax  which  adheres  to  the  wire.  What  is  the  first  effect 
of  this,  and  to  what  is  it  due?  (see  Exp.  21/7.)  When 
the  borax  has  fused  to  a  clear,  glasslike  bead,  touch  it, 
while  still  hot,  to  some  particles  of  copper  oxide.  These 
adhere  to  the  hot  bead.  Do  not  let  it  take  up  too  much — a 
very  minute  quantity  suffices ;  and  if  you  have  not  enough 
on  first  trial,  it  is  easy  to  add  more,  but  it  is  not  so  easy  to 
reduce  the  quantity.  Heat  again  to  fuse  the  bead  with 
the  adhering  copper  oxide.  The  particles  of  the  latter  can 
be  seen  slowly  to  dissolve,  often  with  beautiful  play  of 
colors  on  the  surface  of  the  bead.  Observe  the  color  of 
the  bead,  when  hot,  and  when  cold.  The  bead  should  be 
transparent,  but,  if  too  much  material  has  been  put  in,  it 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS      67 

will  be  opaque,  so  the  color  can  not  be  distinguished.  In 
this  event,  clean  the  wire,  leaving  only  a  fragment  of  the 
bead,  and  add  more  borax.  To  clean  the  wire,  heat  the  229 
bead  hot,  and  quickly  cool  it  in  water.  This  makes  the 
mixture  brittle,  so  that  it  can  be  easily  removed.  To  get 
the  best  results,  in  the  bead  experiments,  the  mouth  blow- 
pipe should  be  used  for  heating.  By  this  means  the  char- 
acter of  the  flame  can  be  so  varied  as  to  cause  the  oxida- 
tion of  the  dissolved  substance,  or  the  removal  of  oxygen 
from  it — i.  e.,  reduction.  These  changes  often  produce 
changes  in  color.  Thus  the  copper  bead  is  blue  when 
heated  in  the  oxidizing  flame,  and  it  has  the  color  of  metal- 
lic copper  in  the  reducing  flame.  (Concerning  the  use  of 
the  blowpipe  see  Appendix  21.) 

Manganese  in  the  bead. — After  seeing  the  color  of  the  228/2 
copper  bead  in  the  oxidizing  and  in  the  reducing  flame, 
make  a  new  bead  and  color  it  with  manganese  dioxide.    Ob- 
serve the  color  in  each  flame. 

5.  CARBON 

C.— 11.91 

Elementary   carbon    exists  in  three  allotropic  forms,  234 
diamond,   graphite,  and   charcoal ;  only  the  last  is  here 
studied. 

Preparation. — Heat  a  small  quantity  of  sugar  on  the  248 
spatula  blade.  It  burns  and  chars.  The  black  charred 
material  consists  mainly  of  carbon.  In  similar  manner 
many  other  substances  show  the  charring  effect  of  heat, 
and  this  is  evidence  of  the  presence  of  carbon  as  a  con- 
stituent in  the  substance.  It  is  due  to  the  removal  in  part 
of  other  constituents,  particularly  hydrogen,  by  combustion, 
the  less  easily  combustible  carbon  being  left  as  residue. 

Place  some  fine  shavings  in  a  dry  test-tube,  fitted  with  254 
a  cork  and  a  short  glass  delivery  tube,  and  apply  the  full 
heat  of  the  flame.     Note  the  appearance  of  moisture  and 


68          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

white  fumes.  Ignite  the  gas  issuing  from  the  tube.  After 
the  heating  observe  the  black  residue  in  the  tube.  This  is 
charcoal.  Note  also  the  liquid,  having  tarry  odor.  Test  it 
with  litmus. 

The  application  of  heat  in  this  manner,  without  free 
access  of  oxygen  or  air,  is  called  dry  or  destructive  distil- 
lation. It  is  applied  on  a  large  scale  to  the  production  of 
various  substances  from  wood,  and  likewise  to  the  produc- 
tion of  illuminating  gas  and  other  substances  by  the  de- 
253  structive  distillation  of  coal.  Heat  a  little  soft  coal  in  a 
test-tube,  as  in  No.  254. 

Properties  of  Carbon  ( Charcoal) 

254/1  Porosity. — Holding  a  piece  of  charcoal  in  the  tongs, 
plunge  it  beneath  the  surface  of  some  hot  water.  Is  char- 
coal heavier  or  lighter  than  water  ?  Keep  it  under  hot 
water  for  a  considerable  time.  Does  it  finally  sink  in  the 
water  ? 

255  Absorptive  power.— Generate  a  very  little  hydrogen  sul- 
phide, using  a  piece  of  iron  sulphide  not  larger  than  a  bean 
and  a  few  drops  of  hydrochloric  acid,  and  collecting  the 
gas  in  a  dry  bottle  covered  with  a  glass  plate  (Appendix, 
19,  V).  Drop  into  this  a  piece  of  charcoal,  previously 
heated  for  a  few  seconds  in  the  gas  flame.  Set  this  aside 
with  the  cover  on,  and  some  time  later  observe  by  odor  if 
the  gas  has  been  absorbed  by  the  charcoal. 

255/1  In  a  beaker  containing  water,  colored  by  a  few  drops  of 
potassium  permanganate  solution,  place  a  small  quantity  of 
boneblack  (animal  charcoal),  boil  for  a  few  minutes,  then 
filter.  Does  the  filtrate  lose  its  color  ?  Is  the  color  re- 
moved by  filtering  simply,  without  the  use  of  the  charcoal  ? 
257  Combustion. — Does  the  substance  burn?  Does  it  burn 
with  a  flame  ?  Why  not  ? 

257/1  Product  of  combustion, — Ignite  a  piece  of  charcoal  in  the 
flame  until  it  is  well  aglow,  then  drop  it  into  a  bottle  and 
cover  the  latter  with  a  glass  plate.  When  the  coal  is  ex- 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS      69 

tinguished,  either  take  out  the  remaining  charcoal  or  invert 
the  bottle  over  another  bottle,  pouring  thus  the  heavy  gas 
from  the  first  into  the  second  bottle  and  leaving  the  char- 
coal. Next  pour  into  the  second  bottle  some  lime-water 
(calcium  hydroxide  solution,  Ca02H2)  and  shake  the  con- 
tents. The  white  precipitate  is  calcium  carbonate,  CaC03, 
and  its  formation  may  generally  be  taken  as  evidence  of 
carbon  dioxide,  which  is,  in  fact,  the  combustion  product  of 
carbon.  Write  the  equation  for  the  formation  thus  of  cal- 
cium carbonate. 

Reducing  power.— Make  a  shallow  hole  in  a  piece  of  257/2 
charcoal,  place  in  this  a  small  quantity  of  litharge  (lead 
oxide),  and  turn  the  flame   (reducing)  of  the  blowpipe 
upon  this  (see  Appendix,  21,  II).     Describe  and  explain 
what  takes  place. 

5a.  Carbon  Dioxide,  C02 

Preparation. — Use  calcium  carbonate  and  hydrochloric  261 
acid  in  the  generator.     Collect  the  gas  by  upward  displace- 
ment of  air  (Appendix,  19,  Y)  in  the  small  collecting  bot- 
tles. 

As  to  solubility.— Test  as  in  Exp.  204.  262 

As  to  combustion  and  specific  gravity. — Plunge  the  lighted  263 
taper  slowly  into  a  bottle  filled  with  the  gas. 

Place  the  lighted  taper  in  one  bottle,  and  pour  upon  it 
the  heavy  gas  from  a  second  bottle.  Holding  a  piece  of 
magnesium  ribbon  in  the  tongs,  ignite  it  at  the  flame  and 
plunge  it  into  a  bottle  well  filled  with  the  gas.  What  is 
the  white  powder  seen  in  the  bottle  after  this  experiment  ? 
What  is  the  black  substance  ?  Why  does  it  retain  some- 
what the  form  of  the  ribbon  ? 

As  to  acid  reaction. — Test  the  action  on  wet  blue  litmus  264 
paper. 

As  to  reaction  with  lime-water  (calcium  hydroxide  solu-  265 
tion). — Collect  some  of  the  gas  in  a  test-tube,  pour  in  some 

lime-water,  and  shake.     Pass  in  repeatedly  more  of  the  gas 
22 


70          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

until  the  precipitate  at  first  formed  nearly  or  quite  disap- 
pears. Then  boil  the  contents  of  the  tube.  Explain  the 
reprecipitation. 

265/1  EXPLANATORY  NOTE. — Excess  of  carbon  dioxide  in  water  forms 
with  calcium  carbonate  an  acid  carbonate  which  is  soluble  in  water. 
This  compound  is  broken  up  at  the  temperature  of  boiling  and  the  ex- 
cess of  carbon  dioxide  is  expelled,  in  consequence  of  which  the  insol- 
uble calcium  carbonate  reappears.  Many  natural  waters  contain  this 
acid  carbonate  of  calcium  or  of  other  bases,  and  therefore  become  tur- 
bid and  deposit  sediment  by  boiling.  Test  some  sample  of  natural 
water  for  this  effect.  See  also  Part  I,  No.  271. 

* 

267  Carbon  dioxide  in  the  breath. — Through  a  glass  tube  blow 
air  from  the  lungs  into  some  li  le-water. 

5d.  The  Hydrocarbons 
Methane,  CH± 

276  Preparation. — Take  about  equal  bulks  of  lime,  CaO,  and 
of   sodium   acetate,   ^N"aC2H302 ;  pulverize  and   mix   them 
thoroughly  in  the  mortar ;  put  some  of  the  mixture  in  a 
dry  test-tube  (about  three  quarters  full),  which  is  provided 
with  a  cork  and  delivery  tube  ;  support  this  on  the  iron 
ring,  heat,  and  collect  the  gas  over  water  in  test-tubes. 

277  Properties. — Examine  the  gas  as  to  color,  odor,  solubil- 
ity in  water,  and  action  on  litmus  (after  the  sample  of  gas 
has  been  shaken  with  w<iter).     Test  for  combustibility  by 
igniting  a  test-tubeful  at  the  flame  ;  then  test  for  a  product 
of  combustion  by  pouring  some  lime-water  into  the  tube  in 
which  the  gas  has  quietly  burned,  and  shaking.     What  are 
the  products  of  combustion  ?     The  combustibility  may  be 
tested  also  by  igniting  the  gas  at  the  end  of  the  delivery 
tube. 

Acetylene,  C2Pf2 

280  Preparation. — Put  three  or  four  lumps  of  calcium  car- 
bide, CaC2,  in  the  gas  generator,  with  enough  alcohol  to 
cover  the  end  of  the  thistle-tube.  Add  water  through  the 


DESCRIPTION   OF  ELEMENTS  AND  COMPOUNDS      71 

thistle-tube,  a  few  drops  at  a  time,  so  as  to  regulate  the 
flow  of  gas,  and  collect  the  gas  over  water  in  test-tubes  as 
for  methane. 

Properties. — Examine  as  to  color,  odor,  solubility  in  281 
water,  and  action  on  litmus,  as  with  methane.  Test  as  to 
combustibility  by  igniting  a  test-tubeful  of  the  gas  at  the 
flame,  then  mix  air  with  acetylene  in  a  test-tube  and  ignite. 
Do  not  try  to  ignite  the  gas  at  the  delivery  tube  without 
the  precautions  taken  with  hydrogen  (testing  a  small  sam- 
ple and  throwing  the  towel  over  the  generator),  for  a  mix- 
ture of  acetylene  and  air  may  be  very  explosive. 

Describe  what  takes  place  in  the  generator,  also  the  appearance  of   2 8 I/a 
calcium  carbide.    Is  the  latter  combustible?    Allow  a  lump  of  it  to  lie 
exposed  to  the  air  for  twenty-four  hours.     Is  it  deliquescent?    Is  it 
hygroscopic  1    Test  the  liquid  left  in  the  generator  with  pink  litmus. 
The  reaction  in  the  generator  is  thus  expressed  : 

CaC2  -f  H20  =  C2H2  +  CaO. 

CaO  +  H2O  =  Ca02H2  (calcium  hydroxide). 

5e.  Flame 

Flame  is  simply  gas,  burning  freely.  A  non-volatile  284 
combustible  like  carbon  burns  without  flame.  To  observe 
some  of  the  characteristics  of  flame,  use  the  Bunsen  burner, 
turned  low,  and  the  air  shut  off.  Note  the  three  different 
portions  of  the  flame  :  First,  the  outer  cone,  pale  blue,  vis- 
ible only  at  the  base  of  the  cone,  where  the  light  is  feeble ; 
second,  the  bright  luminous  cone  ;  third,  the  dark  interior 
cone.  In  the  outer  cone  the  combustion  is  complete,  since 
there  is  free  access  of  air.  In  the  middle  luminous  cone  the 
combustion  is  incomplete,  since  the  air  does  not  penetrate 
so  far  ;  but  the  temperature  is  high,  and  under  these  con- 
ditions the  carbon-containing  constituents  of  the  gas  un- 
dergo chemical  change  somewhat  as  seen  in  the  destructive 
distillation  of  wood.  This  results  in  the  separation  of 
more  or  less  carbon  as  very  small  solid  particles.  These 
are  raised  to  a  high  temperature,  white  heat  (incandescence), 


72          ELEMENTARY   PRINCIPLES  OP  CHEMISTRY 

before  they  come  to  the  outer  cone,  where  they  hum  to 
carbon  dioxide. 

285  Hold  a  cold  object,  like  a  porcelain  dish,  in  this  flame, 
and  some  of  the  carbon  is  deposited  thereon  (as  soot)  before 
it  can  reach  the  air  and  burn. 

286  The   inner  dark  cone  contains  unburned  combustible 
gas,  and  the  temperature  is  much  lower.     Insert  the  open 
end  of  a  narrow  glass  tube  in  this  cone,  and  the  unburned 
gas  may  be  drawn  off  and  ignited  at  the  upper  end  of  the 
tube.     Quickly  thrust  the  head  of  a  match  through  the 
outer  cones  and  into  the  inner  one.     It  does  not  take  fire 
while  held  there,  since  the  temperature  is  comparatively 
low  and  there  is  no  air  ;  but  the  wood  of  the  match  quickly 
burns  at  the  edge  of  the  flame.     A  piece  of  wire  thrust 
horizontally  through  the  flame  is  seen  to  become  luminous 
first  where  it  cuts  the  outer  cones,  while  the  portion  in  the 
inner  cone  remains  dark  for  a  few  seconds. 

287  With  a  few  trials,  a  card,  or  a  sheet  of  stiff  paper  may 
be  lowered  directly  down  upon  the  flame  and  quickly  re- 
moved without  taking  fire,  but  it  will  show  a  ring  of  scorch- 
ing where  it  has  cut  the  outer  cones.     Lower  a  piece  of  wire 
gauze  down  upon  the  flame,  and  the  dark  central  portion 
and  the  luminous  ring  are  plainly  seen. 

288  In  this  experiment  with  the  gauze  it  is  seen  that,  al- 
though the  gas  is  free  to  pass  through  the  gauze,  the  flame 
is  only  on  the  lower  side  of  it.     The  gas  above  the  gauze 
may  be  reignited  with  a  match. 

Bring  the  gauze  squarely  down  upon  the  flame  quite  to 
the  burner,  and  the  flame  may  thus  be  completely  extin- 
guished. Or,  thrust  the  gauze  through ,  the  flame  horizon- 
tally and  close  to  the  burner  so  that  there  is  no  flame  un- 
derneath it,  then  raise  it  to  the  tip  of  the  cone,  and  the 
flame  is  likewise  extinguished. 

289  These  effects  are  due  to  the  fact  that  the  gauze,  being  a  good  con- 
ductor of  heat,  reduces  the  temperature  of  the  gas  below  its  point  of 
ignition.     A  valuable  application  of  the  fact  is  seen  in  the  safety  lamp, 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS      73 

invented  by  Sir  Humphry  Davy,  which  miners  carry  in  coal  mines 
where  there  are  combustible  gases  and  where  there  is  consequently 
danger  of  explosive  ignition  by  the  lamp.  The  lamps  are  inclosed  by 
a  chimney  of  wire  gauze  which  permits  air  to  pass  in,  but  no  flame  to 
pass  outward. 

Effect  of  temperature  on  luminosity. — The  fact  that  the  290 
lowering  of  temperature  lowers  also  the  luminosity  of  flame 
may  be  seen  by  bringing  against  the  flame  a  porcelain  dish, 
or,  better,  an  iron  plate.     The  bright  portion  almost  disap- 
pears, and  hardly  more  than  the  pale  blue  is  seen. 

The  Bunsen  flame. — By  opening  the  valves  at  the  base  of  291 
the  chimney,  so  that  air  enters  and  mingles  with  the  gas  be- 
fore it  burns,  the  character  of  the  flame  is  greatly  changed. 
The  presence  of  air  in  the  interior  of  the  flame  brings  about 
more  complete  combustion,  the  solid  particles  of  carbon 
do  not  separate,  luminosity  nearly  disappears,  and  no  soot 
is  deposited  on  cold  objects.  The  luminosity  may  be  mo- 
mentarily restored  by  blowing  any  fine  dust  into  the  flame, 
such  as  iron  dust,  charcoal,  or  sodium  carbonate. 

The  reduction  of  luminosity  is  not  dependent  on  com-  292 
plete  or  increased  combustion,  since  a  gas  containing  no  oxy- 
gen, such  as  nitrogen,  produces  the  effect,  if  mixed  with  the 
gas  before  burning.     In  this  case  dilution  and  consequent 
reduction  of  temperature  probably  bring  about  the  result. 

Recall  in  this  connection  the  character  of  the  flame 
made  by  the  use  of  the  mouth  blowpipe.  (See  No.  229, 
Part  II,  and  Appendix,  21.) 

6.  NITROGEN 

N.-13.93 

Preparation. — The  air  is  mainly  a  mixture  of  nitrogen  308 
and  oxygen,  and  the  removal  of  the  latter  gives  the  most 
available  method  of  preparing  nitrogen. 

On  a  crucible  lid,  resting  on  a  flat  cork,  and  floating 
on  the  water  in  the  tank,  place  a  small  piece  of  phosphorus. 


74          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

Bringing  the  cork  over  the  bridge  of  the  tank,  ignite  the 
phosphorus  and  invert  a  beaker  over  the  latter,  letting  the 
beaker  rest  upon  the  bridge.  The  phosphorus  burns  with  a 
white  smoke,  which  is  the  pentoxide  of  phosphorus  (P205), 
and  this  is  slowly  absorbed  by  the  water.  The  water  rises 
in  the  beaker,  taking  the  place  of  the  oxygen  thus  removed, 
and  the  gas  left  is  nitrogen.  This  may  be  poured  upward 
under  water  into  another  beaker  or  collecting  bottle,  and 
the  operation  repeated  until  sufficient  gas  is  obtained. 

309  Properties. — Describe  the  gas,  testing  in  the  usual  way 
as  to  solubility  in  water,  as  to  action  on  red  and  on  blue 

310  litmus  paper,  and  as  to  combustion  with  the  taper. 

310/1  NOTE. — Phosphorus  must  be  handled  with  the  greatest  care,  as  it 

ignites  very  easily,  and  burns  made  by  it  are  very  painful  and  difficult 
to  heal.  It  should  never  be  cut  except  while  it  is  under  water ;  the 
piece  to  be  ignited  should  be  gently  touched  with  filter  paper  to  take 
up  the  adhering  water.  After  the  generation  of  nitrogen,  any  phos- 
phorus left  adhering  to  the  lid  should  be  carefully  scraped  off  with  the 
spatula  and  completely  burned,  so  that  there  shall  be  positively  no 
phosphorus  left  unconsumed. 

6a.   Nitrogen  Monoxide  or  Nitrous  Oxide,  N20 

312  Preparation. — Use  the  flask  fitted  with  a  stopper,  and 
with  a  rubber  and  glass  delivery  tube.     Place  in  this  a 
charge  of  solid  ammonium  nitrate,  NH4N03,  considerably 
more  than  enough  to  cover  the  bottom  of  the  flask.     Sup- 
port the  latter  on  the  asbestos  board  and  iron  stand.     It  is 
well  to  pass  the  neck  of  the  flask  through  the  small  ring 
to  prevent  its  falling  over.    Apply  heat,  slowly  at  first,  until 
a  layer  of  melted  salt  covers  the  bottom  of  the  flask.     As 
the  heating   continues  the  salt  apparently  boils;  this  is 
really  decomposition,  and,  when  it  is  well  started,  the  flame 
should  be  removed  lest  the  action  become  too  violent.    Col- 
lect the  gas  over  water.     Eemove  the  delivery  tube  from 
the  water  before  the  current  of  gas   ceases.     The  gas  is 

313  nitrogen  monoxide.     Describe  it,  testing  in  the  usual  man- 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS      75 

ner  as  to  solubility,  action  on  litmus  paper,  and  relation  to  314 
combustion. 

EXPLANATORY  NOTE. — Ammonium  nitrate  is  decomposed  by  heat 
into  nitrogen  monoxide  and  water,  and  the  reaction  liberates  heat. 
Write  the  equation. 

6b.   Nitrogen  Dioxide  or  Nitric  Oxide,  NO 

Preparation. — As  in  Exp.  47/b.  317 

Examine  as  to  solubility.     After  shaking  in  a  test-tube  318 
with  water,  slip  a  crystal  of  ferrous  sulphate  into  the  test- 
tube,  opening  it  under  water,  and  shake  again. 

As  to  action  on  litmus. — This  can  be  observed  only  by  318/1 
slipping  the  litmus  paper  under  water  into  the  tube  or 
bottle  containing  a  sample  of  the  gas,  since  contact  with 
air  would  entirely  change  its  character. 

As  to  combustion. — The  usual  test  with  the  taper  can  318/2 
only  be  applied  in  opening  the  bottle  to  the  air,  hence  the 
observed  property  really  belongs  to  nitrogen  tetroxide  or 
to  a  mixture  of  the  two  oxides. 

Make  the  combustion  test  likewise  with  a  piece  of 
ignited  magnesium  ribbon. 

Save  a  portion  of  this  gas  for  the  next  experiment. 

6c.    Nitrogen  Trioxide  or  Nitrous  Anhydride,  N203 

No  experiments.  3^9  ^0 

321 
6d.   Nitrogen  Tetroxide  or  Peroxide,  N20±  or  N02 

Compare  Experiments  47/i  and  47/2. 

Pass  some  air  into  the  bottle  containing  a  sample  of 
nitric  oxide.     Note  the  color,  solubility,  and  action  on  blue  322  to 
litmus  paper  of  the  tetroxide  thus  produced.  324 

6e.   Nitrogen  Pentoxide  or  Nitric  Anhydride,  N2Q5 

No  experiments.  335 


f  6          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


6f.   Nitric  Acid,  HN03 

329  Preparation. — It  is  made  by  the  combination  of  nitrogen 
pentoxide  and  water  which  takes  place  on  contact ;  also  by 
adding  sulphuric  acid  to  a  nitrate — for  example,  potassium 
nitrate — and  distilling  the  nitric  acid  thus  liberated  from 
the  salt.  (See  Appendix,  18  B.)  What  is  the  other  product 
in  this  reaction  ? 

331  Properties. — Eecall  the  reactions  between  nitric  acid  and 
ferrous  sulphate  (Exp.  317),  and  zinc  (Exp.  41/2)  and  tin 
(Exp.  144). 

Neutralize  about  one  half  test-tubeful  of  nitric  acid 
from  the  side  table  (this  is  really  a  solution  of  nitric  acid 
in  water,  about  63  per  cent)  with  ammonium  hydroxide,  con- 
centrate, and  crystallize  the  salt. 

331/1  Take  a  few  of  these  crystals,  or,  without  waiting  for 
these,  take  some  of  the  substance  from  the  side  table,  and, 
heating  on  the  spatula  blade,  touch  a  glowing  coal  to  the 
melted  salt. 

In  similar  manner  use  a  few  crystals  of  sodium  or  potas- 
sium nitrate. 

331/2  Nitrohydrochloric  acid. — Cut  off  a  small  piece  of  your 
platinum  wire.  Boil  this  in  a  test-tube  with  a*few  drops  of 
concentrated  hydrochloric  acid.  Does  it  dissolve?  Pour 
off  the  acid  and  try  if  the  platinum  dissolves  in  concen- 
trated nitric  acid.  Then  add  to  the  latter  a  few  drops  of 
hydrochloric  acid,  and  again  boil.  What  evidence  of  reac- 
tion do  you  see  ?  Does  the  platinum  dissolve  ? 

331/3  EXPLANATORY  NOTE. — In  this  reaction  the  hydrogen  of  the  hydro- 
chloric acid  is  oxidized  to  water  by  the  nitric  acid,  chlorine  is  liberated, 
and  the  lower  oxide  of  nitrogen  produced.  The  reaction  takes  place  only 
when  the  acids  are  concentrated,  and  the  solvent  action  is  due  to  the 
nascent  chlorine.  The  mixture  of  the  two  acids  is  called  nitrohydro- 
chloric  acid,  or  "  aqua  regia,"  as  it  was  named  in  the  early  days  of 
chemistry  because  of  its  powerful  solvent  action  on  gold  and  other 
metals. 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS      77 

6h.  Ammonia,  NH% 

Preparation, — Heat  in  a  test-tube  a  piece  of  flannel  or  334 
other  woolen  stuff.     Note  the  odor  of  the  gas  and  its  action 
on  litmus. 

EXPLANATORY  NOTE. — Wool,  hair,  and  similar  organic  substances 
contain  nitrogen,  as  does  coal  also ;  these,  by  dry  distillation,  yield 
ammonia  or  ammonialike  substances.  Ammonia,  therefore,  is  a  prod- 
uct in  making  illuminating  gas  by  the  distillation  of  coal. 

Rub  together  in  the  mortar,  or  even  in  the  palm  of  the  334/1 
hand,  some  sodium  carbonate  or  some  lime  and  an  ammo- 
nium salt.     What  gas  is  liberated?    "Write  the  equation 
for  the  reaction. 

In  a  flask  fitted  with  stopper  and  delivery  tube,  heat  some  334/2 
ammonium  hydroxide  solution.     Collect  the  gas  in  a  dry 
bottle  ;  it  is  lighter  than  air.    Is  it  soluble  in  water  ?    What  335 
is  its  action  on  litmus  ?    Does  the  taper  or  match  burn  in 
the  gas  ?    Does  the  gas  itself  burn  ?    Test  this  by  holding 
the  tube  which  delivers  the  ammonia  close  to  the  flame,  or 
by  passing  the  gas  into  the  openings  at  the  base  of  the 
chimney.     What  do  you  infer  are  the  products  when  am- 
monia burns  ? 

7.  OXYGEN 

O.— 15.88 

-    4  •  • 

Preparation. — Heat  in  a  test-tube  a  small  quantity  of  352 
potassium  chlorate,  KC103  (about  as  much  as  could  be 
heaped  on  a  copper  cent).  Note  the  phenomenon,  and  test 
the  gas  at  the  mouth  of  the  test-tube  with  a  lighted  splinter 
of  wood,  having  care  that  nothing  drops  into  the  test-tube. 
In  a  similar  manner  heat  about  the  same  quantity  of  man- 
ganese dioxide.  Are  you  able  to  get  evidence  of  oxygen  at 
the  mouth  of  the  tube  ?  Xow  mix  a  little  of  the  chlorate 
and  dioxide,  and  heat  as  before  and  test  the  gas.  Is  the 
gas  obtained  more  readily  with  or  without  the  dioxide  ? 


78          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

To  obtain  the  gas  in  larger  quantity  for  examination  (if 
the  reservoir  supply  is  not  at  hand),  prepare  it  as  in  Exp. 
71  A,  and  collect  in  the  smaller  bottles.  Recall  the  results 
of  Exps.  71  A  and  71/2. 

353  to         Examine  as  to  solubility,  action  on  litmus,  and  relation 
357     to  combustion,  using  a  candle  or  splinter  of  wood  ;  and  if 
further  illustration  is  desired,  use  a  bit  of  sulphur  ignited 
in  the  metal  spoon. 

NOTE. — After  oxygen  is  evolved  from  the  chlorate,  KC103 ,  potas- 
sium chloride  is  left.  If  the  temperature  is  high  enough,  oxygen  is 
obtained  from  the  manganese  dioxide  alone,  as  expressed  in  the  equa- 
tion 

3MnO2  =  Mns04  +  20. 


8.  FLUORINE 

F.— 18.91 

402  The  preparation  of  this  element  is  difficult,  and  it  is 
practically  impossible  as  a  laboratory  experiment. 

Its  compound  with  calcium,  CaF2 ,  is  a  common  mineral, 

405  known  as  calcium  fluoride  or  fluor  spar.  This  is  a  salt  of 
hydrofluoric  acid,  HF.  By  acting  upon  it  with  strong  sul- 
phuric acid,  the  former  acid  is  liberated  as  a  gas. 

CaF2  +  H2S04  =  CaS04  +  2HF. 

40G  The  hydrofluoric  acid  attacks  and  dissolves  glass,  and  is 
used  practically  for  etching.  This  may  be  illustrated  as  fol- 
lows :  Clean  and  dry  a  piece  of  window  glass  (use  one  of  your 
glass  covers) ;  spread  over  it  a  thin  film  of  melted  paraffin, 
using  the  hot  spatula  blade  to  melt  the  latter.  With  the 
point  of  a  pin  or  penknife  expose  the  glass  surface  by  trac- 
ing any  chosen  design  through  the  paraffin.  In  a  shallow 
lead  dish  place  some  powdered  fluor  spar,  and  mix  this  with 
sulphuric  acid  to  a  thin  paste.  A  splinter  of  wood  may 
serve  as  stirrer.  Cover  the  dish  with  the  glass  plate,  the 
protected  side  down,  and  leave  for  twenty-four  hours. 


DESCRIPTION  OF  ELEMENTS  AND   COMPOUNDS      79 

Clean  off  the  paraffin  with  hot  water,  and  the  design  will 
be  found  etched  into  the  glass.  (Scrape  the  content  %  of 
the  lead  dish  into  the  waste  jar.) 


9.  SODIUM 

Na.— 22.88 

The  element  is  supplied  already  prepared.  Describe  its  410 
appearance.  It  decomposes  water  at  ordinary  temperature. 
To  show  this,  wet  a  filter  paper,  spread  it  flat  on  the  table, 
and  lay  on  it  a  piece  of  red  litmus  paper.  Place  on  the 
filter  a  piece  of  sodium,  perhaps  twice  the  size  of  a  pin- 
head.  (Have  care  not  to  touch  sodium  with  wet  fingers.) 
Describe  the  phenomenon.  If  the  sodium  does  not  take 
fire,  let  a  drop  of  water  fall  upon  it  from  a  glass  rod 
or  the  end  of  the  finger.  Note  the  action  on  the  litmus. 
Explain  the  whole  reaction.  (Toward  the  end  of  the  reac- 
tion the  little  globule  of  melted  metal  is  likely  to  snap  off 
the  paper.  Be  careful  that  it  is  not  thrown  in  the  face, 
or  elsewhere,  to  do  harm.) 

9c.  Sodium  Hydroxide  or  Caustic  Soda 

Eecall  what  is  already  known  of  this  substance  from  420 
previous  experiments.  Describe  the  solid  hydroxide.  Make 
a  solution  of  it,  a  stick  4  or  5  centimeters  long  (1J  or  2 
inches),  in  a  beaker  one  half  to  three  quarters  filled  with 
water.  Observe  what  takes  place  during  solution.  Neu- 
tralize about  three  quarters  of  the  solution  thus  obtained 
with  hydrochloric  acid,  filter,  concentrate,  and  crystallize. 
What  is  the  appearance  of  the  crystals  ?  What  is  the  sub- 
stance ?  Write  the  equation  for  the  neutralization. 

With  another  portion  of  the  sodium  hydroxide  solution,   420/1 
observe  and  describe  what  takes  place  on  adding  a  few  drops 
of  it  to  dilute  solutions  of  these  several  salts  in  different 
test-tubes :  Ammonium  nitrate  or  chloride  (heat,  and  note 


80          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

odor),  iron  sulphate,  copper  sulphate,  alum  (i.  e.,  aluminium 
sulphate),  sodium  nitrate,  and  perhaps  other  salts  if  at  hand. 

420/2  EXPLANATORY  NOTE. — Sodium  hydroxide  is  a  base,  and  it  is  at 
least  conceivable  that,  when  added  to  a  salt,  it  might  combine  with  the 
acid  of  the  latter,  forming  a  new  salt  and  leaving  the  base  of  the  origi- 
nal salt  wholly  or  partly  deprived  of  its  acid — i.  e.,  leaving  it  in  the 
condition  of  a  hydroxide.  Now,  if  this  took  place,  and  if  either  the 
new  salt  or  the  new  hydroxide  were  insoluble  in  water,  evidence  of  the 
change  would  be  seen  in  precipitation.  On  the  other  hand,  if  the  new 
substances  were  soluble,  no  precipitate  would  appear,  and  it  might 
be  difficult  to  get  evidence  as  to  the  change.  The  fact  is  that  the 
sodium  salts  are  soluble,  but  the  hydroxides  of  iron,  copper,  and  alu- 
minium are  insoluble,  and  are  the  precipitates  which  are  seen  in  these 
reactions.  Ammonium  hydroxide  is  soluble,  hence  no  precipitate  is 
seen  with  the  ammonium  salts ;  but  if  the  mixture  is  boiled,  ammonia  is 
liberated,  showing  the  presence  of  the  hydroxide  in  the  solution.  With 
sodium  nitrate,  of  course,  there  is  no  reaction.  The  reaction  with  iron 
sulphate  is  expressed  in  saying  sodium  hydroxide  and  iron  sulphate 
become  iron  hydroxide  and  sodium  sulphate.  With  this  information 
let  the  student  complete  the  second,  third,  and  fourth  of  the  following 
equations,  in  which  the  precipitates  are  underscored  : 

SNaOH  +  FeS04  =  Fe02H2  +  Na2S04 
/    NaOfe  +  CuS04  =  CuQ2H2 
<£>  NaOH  +  A12(S04)3  =  A1206H6  • 
NaOH  +  NH4N03  =  NH4OH  + 
NaOH  +  NaN03  =  no  reaction. 

10.   MAGNESIUM 

Mg.— 24.10 

445  The  element  itself  is  supplied.     Describe  its  appear- 
ance and  recall  whatever  has  been  learned  of  it  in  previous 
experiments.     By  observation  answer  the  following  ques- 
tions :  Does   magnesium  melt  ?    Does  it  burn  ?     What  is 

446  the  appearance  of  the  product  of  combustion,  MgO  ?    Does 
the  oxide  dissolve  in  water  ?    In  hydrochloric  acid  ? 

Using  strips  of  the  ribbon,  one  or  two  centimeters  long 
(one  half  to  three  quarters  of  an  inch),  ascertain  if  magne- 
sium decomposes  cold  water  or  boiling  water.  (Have  a 


DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS      81 

piece  of  red  litmus  paper  in  the  water.)  Does  the  hydrox- 
ide act  as  base  or  acid  ?  Does  the  metal  dissolve  in  very 
dilute  hydrochloric  acid  ?  In  very  dilute  nitric  acid  ?  In 
very  dilute  sulphuric  acid  ? 

Make  a  dilute  solution  of  magnesium  sulphate  (MgS04),  446/1 
by  dissolving  the  dry  salt  (from  the  side  table),  a  lump 
about  the  size  of  a  pea,  in  a  test-tube  nearly  filled  with 
water.  Add  to  a  small  portion  of  this  solution  a  few  drops 
of  sodium  hydroxide  solution.  What  is  the  precipitate? 
(See  No.  420/2.)  In  a  similar  manner  add  to  diiferent  por- 
tions of  the  magnesium  sulphate  solution  a  few  drops  of 
solutions  of  these  several  substances  :  ammonium  hydrox- 
ide, ammonium  chloride,  ammonium  carbonate,  sodium 
carbonate,  sodium  phosphate.  Magnesium  hydroxide,  car- 
bonate, and  phosphate  are  insoluble.  With  this  informa- 
tion complete  the  following  equations  : 

Mg  +  0  = 

Mg  +1H20  = 

Mg  -fjHCl  .=  Mg012  - 

Mg  +  H2S04  =  MgS04  +  *  *          S0« 

MgS04  -+fNaOH  ?*&&* 

MgS04  +  Na2C03  =  MgC08  + 

MgS04  +  *Ta2HP04  =  MgHP04 


What  is  the  valence  of  magnesium  ? 
11.   ALUMINIUM 

Al.— 26.9 

The  element  itself  is  supplied.     Describe  its  appearance.   451  to 
By  trial  learn  if  it  melts,  and  if  it  burns.     Does  it  decom-     454 
pose  water,  cold  or  boiling  ?    Does  it  dissolve  in  dilute  hy- 
drochloric acid  ?    In  dilute  nitric  ?    In  dilute  sulphuric  ? 
In  dilute  solution  of  sodium  hydroxide  (boil)  ?    What  is 
the  behavior  of  aluminium  sulphate  (alum)  in  dilute  solu- 
tion toward  these  several  substances  also  in  dilute  solution  : 


82          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

sodium  hydroxide  (first  in  small  proportion  then  in  excess), 
ammonium  hydroxide,  ammonium  chloride,  sodium  carbon- 
ate, sodium  phosphate  ?  Aluminium  hydroxide  and  phos- 
phate are  insoluble  in  water  ;  the  chloride  is  soluble.  The 
hydroxide  dissolves  in  excess  of  sodium  hydroxide,  forming 
a  soluble  compound  in  which  the  former  acts  as  acid,  and 
the  latter  as  base. 

12.   SILICON 

Si.— 28.2 

EXPLANATORY  NOTE. — It  is  not  practicable  to  supply  the  element — 
not,  indeed,  even  to  show  it.     The  dioxide,  Si02,  is,  however,  abundant 

473  as  common  sand.     This  oxide  acts  as  an  acid-former,  and  when  brought 
in  contact  with  fused  sodium  carbonate  it  liberates  carbon  dioxide  and 
combines  with  the  bafte,  forming  a  silicate,  the  composition  of  which 
may  be  sufficiently  indicated  by  the  formula  Na2OSi02  or  Na2Si03 . 
This  is  soluble  in  water,  and  when  hydrochloric  acid  is  added  to  the  solu- 
tion the  silicic  acid,  H2OSi02 ,  in  turn  is  liberated  and,  being  insoluble 
in  water,  is  precipitated.     The  precipitate  is,  however,  soluble  in  the 
hydrochloric  acid,  probably  without  chemical  change,  and  may  be  repre- 
cipitated  by  neutralizing  the  acid,  HC1,  with  ammonium  hydroxide. 

474  Place  a  few  grains  of  sand  (powdered  glass  may  be  used 
in  the  same  way)  in  a  shallow  hole  of  a  piece  of  charcoal, 
cover  the  sand  with  five  or  six  times  its  bulk  of  sodium  carbon- 
ate, fuse  thoroughly,  using  the  blowpipe.    Note  the  minute 
bubbles.     What  causes  them  ?    After  sufficient  fusion,  re- 
move the  mixture  from  the  charcoal,  treat  with  hot  water, 
filter,  acidulate  with  hydrochloric  acid,  using  litmus  paper, 
and  boil.     If  the  precipitate  does  not  appear,  add  ammo- 
nium hydroxide  to  slight  alkalinity,  and  boil  again.     De- 
scribe the  appearance  of  the  precipitated  silicic  acid,  H2Si03 . 
Filter  the  precipitate  and  dry  it. 

Complete  the  equations  : 

Si02  +  Na2C03  =  NapSiOs  + 
Na8SiOs  -4/HQ1  =  H8SiOs  +  *  (' 
H3Si03(heated)  =  SiOg+  ^  c 


DESCRIPTION. OF  ELEMENTS  AND  COMPOUNDS      83 
13.   PHOSPHORUS 

P.-30.8 

Recall  the  use  already  made  of  phosphorus.  It  must  be  handled 
with  the  utmost  caution,  because  of  the  danger  of  ignition.  Burns 
produced  by  it  are  painful  and  difficult  to  heal. 

Describe  the  appearance  of  yellow  phosphorus.  486 

Place  the  porcelain  lid  and  cork  on  a  dry  glass  plate.  487 
On  the  lid  place  a  small  fragment  of  phosphorus.  Ignite 
the  latter  and  cover  it  with  a  dry  beaker.  The  oxide 
formed  is  mainly  Pg05.  Describe  the  burning  and  the 
product.  Let  the  white  oxide  settle  upon  the  glass  plate. 
Observe  the  marked  deliquescence.  Touch  blue  litmus 
paper  to  the  oxide.  Is  it  an  acid-  or  a  base-forming  oxide  ? 

Phosphorus  a  reducing  agent, — Into  a  test-tube  about  one  487/1 
third  filled  with  a  dilute  solution  of  silver  nitrate,  AgN03 , 
drop  a  small  piece  of  yellow  phosphorus,  about  twice  the  size 
of  a  pinhead.  Le1^  stand  for  twenty-four  hours.  Minute 
crystals  of  metallic  silver  will  be  seen  at  the  bottom  of  the 
test-tube.  The  liquid  may  be  drained  off  and  the  crystals 
fused  on  the  charcoal  or  asbestos  to  a  small  globule  of  silver. 

Describe  the  appearance  of  the  red  phosphorus,  and  490 
compare  it  with  the  yellow  as  to  inflammability. 

EXPLANATORY  NOTE. — Phosphorus  pentoxide  combines  with  water   494  to 
in  three  different  ratios,  forming  three  phosphoric  acids,  thus :  496 

P20B  +  3H20  =  2H3P04  —  orthophosphoric  acid. 
Pa06  +  2H20  =  H4P207  =  pyrophosphoric  acid. 
P206  +  H20  =  2HP03  =  metaphosphoric  acid. 

When  sodium  orthophosphate,  Na2HP04,  is  sufficiently  heated,  it  be- 
comes the  pyrophosphate,  Na4P207 .  Both  are  soluble  in  water,  but  the 
latter  does  not  immediately  pass  back  to  the  orthophosphate  when  in 
contact  with  water. 

Taking  a  fragment  of  crystallized  sodium  orthophos- 
phate, Na2HP04,  fuse  it  on  charcoal,  keeping  it  fused  for 
some  minutes.  Eemove  the  salt  when  cool,  dissolve  in  a 


84          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

little  hot  water,  filter,  and  to  the  solution  add  a  few  drops 
of  silver  nitrate  solution.  Describe  the  precipitate,  Ag4P207. 
Dissolve  a  small  piece  of  the  sodium  orthophosphate  in 
water,  and  add  to  this  a  few  drops  of  silver  nitrate.  De- 
scribe this  precipitate,  Ag3P04.  How  has  the  fusion 
changed  the  orthophosphate  ?  Write  the  equation  for  the 
reaction  of  fusion,  also  for  the  precipitations. 


14.  SULPHUR 

S.-31.83 

509  Sulphur  was  studied  in  considerable  detail  at  the  very  first  of  the 
course,  and  it  would  seem  unnecessary  to  repeat  the  experiments  here. 
They  should  at  least  be  recalled,  and  it  may  be  well  to  write  out  a  de- 
scription from  the  earlier  observations.    These  items  may  serve  as  out- 
line :  specific  gravity,  as  to  solubility  in  water,  color,  hardness,  crys- 
talline form  from  fusion,  from  solution  in  carbon  disulphide,  plastic 
allotropic  form,  fusion,  combustion,  behavior  with  iron,  with  zinc,  and 
with  lime. 

510  Hydrogen  sulphide,  HaS,  also  was  studied  somewhat,  and  these  items 
and   should  be  recalled :  formation  by  the  action  of  hydrochloric  acid  on 

511  metallic  sulphides,  odor  of  gas,  action  on  paper  wet  with  lead  acetate, 
behavior  with  strong  nitric  acid. 

512  The  sulphides. — Hydrogen  sulphide  is  an  acid,  and  in 
combining  with  ammonium  hydroxide  it  forms  the  acid 
sulphide,  NH4HS,  or  the  normal  (NH4)2S.     Persulphides 
also  are  formed,  such  as  (NH4)2S2  and  (NH4)2S3,  the  coeffi- 
cient of  S  being  2  or  more.     The  common  reagent,  yellow 
ammonium  sulphide,  much  used  in  the  laboratory,  is  made 
by  saturating  ammonium  hydroxide  with  the  gas,  H2S.     It 
therefore  contains  more  or  less  persulphide.     With  this 
solution  of  ammonium  sulphide  make  the  following  experi- 
ments and  describe  the  results :  Add  a  small  portion  to 
these  several  solutions :  hydrochloric  acid,  sodium  nitrate, 
magnesium  sulphate,  alum,  iron  sulphate,  copper  sulphate, 
lead  acetate,  and,  if  at  hand,  to  solutions  containing  arsenic, 
antimony,  and  cadmium. 


jtfr^        A  p 

DESCRIPTION  OF  ELEMENTS  ANJT  COMg0T?BS)S  r 
Complete  the  following  equations: 


S  +  MgS04  = 
S  +  AL(SOJ3  =  A1206H6 
S  +  FeS04  =  FeS 
S  +  CuS04  =  CuS 
What  is  the  valence  of  sulphur  in  hydrogen  sulphide  ? 
Sulphur  dioxide.  —  This  substance  is  formed  by  burning  515 
sulphur,  but  more  conveniently  by  the  action  of  hydro- 
chloric acid  on  sodium  sulphite,  Na2S03.     Place  some  of 
the  latter  in  the  generator,  add  the  acid  gradually,  and 
collect  the  gas  by  dry  displacement,  since  it  is  soluble  in 
water  and  heavier  than  air.     Test  the  gas  for  odor  (it  is  516 
very  irritating),  solubility,  action  on  the  burning  candle  or 
match,  weight  as  compared  with  air  (as  in  the  experiment 
with  carbon  dioxide  Xo.  263),  and  action  on  litmus  paper, 
both  brief  and  somewhat  prolonged. 

To  a  portion  of  sodium  sulphite  solution  add  a  few  517 
drops  of  potassium  permanganate,  KMn04,  and  to  another 
portion  add  a  crystal  of  iodine.    Describe  what  takes  place. 

Sulphur  dioxide,  sulphurous  acid,  H2S03,  and  the  sulphites,  all  tend 
more  or  less  readily  to  take  up  oxygen  and  become  the  trioxide,  sul- 
phuric acid,  H2S04,  and  the  sulphates  respectively;  the  former  there- 
fore act  as  reducing  agents. 

Complete  these  equations  :  517/1 


H2S03 
3- 

0  = 


Na2S03  +  0  =  nw  *  ^° 

JSTa2S03  +  H20  4JI  =  2HI  +,)4  •> 

@20/SWOv  +  H^T  =  2KOH  +  2MnO 
23  ^ 


86          ELEMENTARY   PRINCIPLES  OF  CHEMISTRY 

519  Sulphuric  acid, — With  sulphur  trioxide  it  is  not  practi- 
cable to  work,  but  its  compound  with  water,  sulphuric  acid, 
H2O.S03,  or  H2S04,  is  a  common  reagent.  Describe  its 
appearance. 

Taking  about  one  half  of  a  test-tubeful  of  the  concen- 
trated sulphuric  acid,  dilute  it  with  about  three  times  its 
volume  of  water.  Note  what  takes  place.  CAUTION  : 
Make  it  a  rule  in  diluting  strong  sulphuric  acid  always  to 
add  the  acid  to  the  water  slowly  and  with  constant  stirring, 
and  never  the  water  to  the  acid.  Why  ? 

521  Taking  three  equal  portions  of  the  dilute  acid,  neutral- 
ize one  portion  with  a  solution  of  sodium  hydroxide,  filter, 
concentrate,  and  crystallize.  Neutralize  the  second  por- 
tion in  the  same  way,  and  to  it  add  the  third  portion ;  filter, 
concentrate,  and  crystallize.  Compare  the  crystallizations ; 
dry  a  sample  of  each  product  on  filter  paper,  and  test  it 
with  litmus  paper,  red  and  blue.  Let  a  sample  of  each  lie 
exposed  to  the  air  for  twenty-four  hours. 

519/1  To  show  the  tendency  of  strong  sulphuric  acid  to  re- 
move the  constituents  of  water :  having  a  small  quantity 
of  the  acid  in  a  test-tube,  drop  into  it  a  splinter  of  pine 
wood,  or  a  piece  of  filter  paper.  What  takes  place  after 
some  minutes? 

521/1  Sulphate  changed  to  sulphide  :  taking  a  crystal  of 
sodium  sulphate  from  the  side  table  or  from  the  product 
of  the  preceding  experiment,  No.  521,  fuse  it  on  the  char- 
coal, first  adding  some  sodium  carbonate  (use  the  reducing 
flame  of  the  blowpipe).  Kemove  the  product  from  the 
charcoal,  lay  it  upon  a  piece  of  filter  paper  wet  with  lead 
acetate,  and  let  a  drop  of  water  fall  upon  it.  What  does 
the  black  stain  indicate  ?  A  silver  coin  may  be  substituted 
for  the  lead  paper. 

521/2  Solubility  of  sulphates. — Add  a  few  drops  of  sodium  sul- 
phate or  of  dilute  sulphuric  acid  to  a  solution  of  lead  ace- 
tate ;  also,  if  at  hand,  to  the  solution  of  a  barium  salt  (e.  g., 
BaCl2),  and  of  a  strontium  salMe.  g. 


.—  '/  '      • 

DESCRIPTION  OF  ELEMENTS  AND  COMPOUNDS      87 

Complete  these  equations  : 

S03-fH20  = 

H2S04  +  NaOH  =  Ka2S04  + 

H2S04  +  NaOH  = 


H2S04  +  BaCl8  =  BaS04 


Na2S04  +  Pb(  A)2  =  PbS04  + 
15.    CHLORINE 

Cl.-35.18 

This  element  is  extremely  disagreeable  to  deal  with  in 
large  quantity.  It  is  best  that  the  illustrative  experiments 
in  the  laboratory  be  only  on  the  test-tube  scale. 

Preparation.  —  Hydrochloric  acid  is  commonly  the  source  529 
of  chlorine.     From  this  it  is   obtained  by  oxidizing  the 
hydrogen  to  water,  and  thus  liberating  the  chlorine.     The 
methods  differ  only  in  the  means  used  to  oxidize. 

(a)  Place  in  a  test-tube  a  small  quantity  of  manganese  529/2 
dioxide,  Mn02,  about  as  much  as  could  be  heaped  on  a  cop- 

per cent.  Add  to  this  about  one  quarter  of  a  test-tubeful 
of  concentrated  hydrochloric  acid  and  warm  gently.  Ob- 
serve cautiously  the  odor,  also  the  effect  on  wet  litmus  530 
paper  of  brief  and  then  of  somewhat  prolonged  exposure 
to  the  gas.  Enough  of  the  gas  may  be  generated  in  the 
test-tube  to  show  its  color,  and  some  of  it  may  be  poured 
into  a  second  dry  tube  (it  is  heavier  than  air)  in  order  to 
test  as  to  its  solubility  in  water. 

Complete  this  equation  by  inserting  the  necessary  co- 
efficients : 

Mn02  +     HC1  =  MnCl2  (sol.  salt)  +      H20  +      01. 

(b)  Place  in  a  test-tube  some  potassium  chlorate,  KC103,  529/1 
about  the  size  of  a  pinhead,  and  add  concentrated  hydro- 
chloric acid,  a  few  drops.     Note  the  evolution  of  gas,  the 


88          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

odor,  color,  etc.     Dilute  with  water.     Does   the  reaction 
continue  ?     Complete  the  equation : 

KC103  +     HC1  =  KC1  (sol.  salt)  +     H20  +     01. 

Hydrochloric  Acid,  HCl 

534  Preparation. — Place  some  sodium  chloride,  NaCl,  in  a 
test-tube  ;  a  lump  about  the  size  of  a  pea  will  serve.  Add 
to  this  a  few  drops  of  concentrated  sulphuric  acid,  H2S04, 
and  warm.  Note  the  odor  of  the  gas,  and  its  action  on 
blue  litmus  paper.  Hold  at  the  mouth  of  the  test-tube  a 
glass  rod  wet  with  ammonium  hydroxide.  What  causes 
the  white  fumes  ? 

The  properties  of  hydrochloric  acid  have  been  illus. 
trated  in  its  repeated  use. 

534/1  Solubility  of  chlorides. — Mix  a  few  drops  of  hydrochloric 
acid,  or  of  sodium  chloride  solution,  with  these  several  salts 
in  dilute  solution  :  lead  acetate,  Pb(C2H302)2 ;  silver  ni- 
trate, AgN03;  mercurous  nitrate  (if  at  hand),  HgN03; 
magnesium  sulphate,  MgS04;  iron  sulphate,  FeS04,  etc. 
The  first  three  of  these  bases  form  insoluble  chlorides. 
The  other  chlorides  are  as  a  rule  soluble. 

Complete  these  equations : 

NaCl  +  H2S04  = 
HCl  +  Pb(C2H302)2  = 
HCl  +  AgN03  = 
HCl  +  HgN03  = 
HCl  +  MgS04  = 

16.    POTASSIUM 


552  If  the  metal  potassium  and  its  hydroxide,  KOH,  are  at 
and  hand,  experiments  with  them  may  be  made  exactly  as  with 

553  sodium  and  sodium  hydroxide.     But  the  results  are  so  en- 
tirely similar  that  the  observations  may  be  omitted. 


DISCRIPTION  OF  ELEMENTS  AND  COMPOUNDS       89 
17.    CALCIUM 

Ca.—  39.7 

The   element  is  not  available   for  these  experiments,  581 
being  difficult  to  obtain,  but  the  oxide,  lime,  CaO,  is  read- 
ily procured.     If  quicklime  is  at  hand,  use  it  to  observe  the 
effect  of  contact  with  water.     If  only  slaked  lime,  Ca(OH)2, 
is  provided,  it  will  serve,  except  for  this  single  observa- 
tion.    Learn  by  experiment  if  calcium  hydroxide  dissolves  582 
in  water.     Does  it  act  as  base  or  as  acid  ?    What  reaction 
takes  place  with  carbon  dioxide  ?    Prepare  a  solution  of 
calcium  chloride,  CaCl2,  by  neutralizing  with  lime  about 
one  third  of  a  test-tubeful  of  the  acid,  and  filtering.     With  584 
this  solution,  observe  the  reactions  with  dilute  solutions  of 
these  several  substances  :  ammonium  hydroxide,  chloride, 
carbonate,  and  oxalate  (NH4)2C204  ;  sodium  phosphate,  and 
sodium   or  potassium  sulphate   or  dilute   sulphuric   acid. 
Complete  the  following  equations  :  .  » 


Qa(OH)2  +  SCI  =     Co 

CaCl2+(NH4)2C03-    ^^3   ' 

CaCl2  +  (NH4)2C204  =  j  <*  IU  * 

CaCl2-fNa2HP04  = 

CaCl2-f]Sra2S04  = 

23.    IRON 

Fe.—  55.6 

Several  experiments  with  iron  and  its  salts  have  already  596 
been  performed,  and  should  be  recalled  here.     With  a  sam- 
ple of  iron,  learn  by  trial  if  it  melts  or  burns  in  the  flame 
of  the  Bunsen  burner  or  in  that  of  the  blowpipe.     Does 
it  decompose  water,  cold  or  boiling  ?    Does  it  dissolve  in  598 
dilute  hydrochloric  acid  (recall  other  experiments)  ?    In 
dilute  nitric  acid  ?    In  dilute  sulphuric  acid  ? 


90          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

Take  about  a  test-tubeful  of  hydrochloric  acid,  dissolve 
in  this  as  much  iron  as  it  will  take  up,  keeping  some  ex- 
cess of  iron  present  (a  nail  serves  well).  Filter,  concen- 

600  trate,  and  crystallize  the  ferrous  chloride. 

As  alternative  with  the  preceding,  dilute  sulphuric  acid 
may  be  used  and  the  ferrous  sulphate  may  be  crystallized. 

To  a  dilute  solution  of  ferrous  salt  freshly  made,  add 

ammonium  hydroxide  solution.     What  is  the  precipitate  ? 

600/1         To  a  dilute  solution  of  ferrous  salt  add  a  few  drops  of 

concentrated  nitric  acid,  boil  a  few  seconds,  then  add  am- 

monium hydroxide  to  alkaline  reaction.     What  is  the  pre- 

601  cipitate?     [Ferric  hydroxide,  Fe2(OH)6  or  Fe(OH)3,  simi- 
lar to   iron   rust.]     What   takes   place   when   solution   of 
ammonium  sulphide  is  added  to  a  ferrous  solution  ?    Re- 
call the  experiment  made  previously  in  studying  the  sul- 
phides. 

EXPLANATORY  NOTE.  —  The  ferrous  salts  when  in  solution  oxidize 
readily  to  ferric  salts  even  by  the  action  of  the  air,  more  quickly  by 
the  action  of  nitric  acid.  The  color  changes  in  consequence,  and  the 
precipitates  with  ammonium  hydroxide  and  other  reagents  are  different. 

Complete  the  following  equations  : 

Fe  +  HOI  =  FeCl2  + 

Fe  +  H2S04  =  FeS04  + 

FeS04  +  HJSTOs  =  Fe2(S04)3  +  NO  + 

FeCl2  +  NH4OH  =  Fe(OH)2  + 


FeCl3  +  NH4HS  =  FeS  + 
FeCl3  +  NH4OH  =  Fe(OH)3 


APPENDIX 


Weighing. — Substances  which  corrode  metal  should  be  1 
weighed  on  glass,  and  general  care  should  be  taken  to  pro- 
tect the  metallic  parts  of  the  balance  from  injury.  Things 
when  weighed  should  not  be  hot,  but  should  be  at  the  tem- 
perature of  the  room.  During  the  more  exact  weighing, 
care  should  be  taken  that  currents  of  air  do  not  interfere 
with  the  swinging  of  the  beam.  The  equilibrium  should 
be  tested  while  the  beam  is  in  motion  by  the  equality  of 
swing  to  either  side  of  the  zero  point,  $,  on  the  scale. 
Generally  the  equilibrium  should  be  tried  with  nothing  in 
the  pans  before  the  actual  weighing.  In  using  balances  of 
the  type  A  or  B  (Fig.  5  or  Fig.  6),  it  is  best  to  put  the  ob- 
ject to  be  weighed  on  the  left-hand  pan,  and  the  weights, 
or  counterpoise,  on  the  right.  The  weights  should  be  placed 
in  the  pan  for  trial  in  regular  succession,  until  one  is  found 
which  is  too  heavy  and  one  which  is  too  light,  and  finally  the 
exact  counterpoise  is  found.  It  is  well  to  read  the  weights 
first  from  the  vacant  places  in  the  box,  record  the  total, 
then  read  from  the  weights  themselves  as  they  are  taken 
from  the  pan,  the  largest  first.  Care  must  be  taken  to 
return  each  weight  to  its  proper  place,  to  guard  against  the 
loss  of  any,  and  to  leave  the  balance  clean  and  in  proper 
condition  for  the  next  weighing. 

The  balance  of  the  type  A  is  for  the  heavier  weighings, 
and  will  hardly  respond  to  less  than  0.2  or  0.3  of  a  gram. 
The  balance  B  should  indicate  0.01  of  a  gram.  The  equilib- 
rium is  tested  by  pressing  down  the  lever,  Z,  which  raises 

91 


FIG.  5. — Balance  A. 


FIG.  6.— Balance  B. 


FIG.  7.— Balance  C. 


Weights. 


FIG.  8. 


FIG.  9. 


FIG.  10. 


APPENDIX 


93 


the  beam  so  that  it  is  free  to  swing.  .  The  balance  C  has 
but  one  pan,  and  the  weights  are  in  the  form  of  rings 
which  slide  along  the  beam  without  removal  therefrom, 
but  when  not  in  use  hang  upont  he  peg,  P.  The  largest 
ring  gives  grams  in  tens,  the  next  smaller  in  units,  the 
third  in  tenths,  and  the  fourth  in  hundredths.  So  the 
total  reading  shown  in  the  figure  is  75.30  grams. 

Heating  a  test-tube,  Fig.  11. — A  strip  of  paper  is  folded  2 
two  or  three  times  upon  itself  and  wrapped  around  the 
test-tube  to  serve  as  holder,  or,  better,  a  strip  of  asbestos  is 
thus  used. 


FIG.  ll. 


FIG.  12. 


Pouring  from  a  reagent  bottle,  Fig.  12. — The  stopper  is  3 
taken  between  the  fingers  of  the  right  or  left  hand  as  pre- 
ferred, and  withdrawn  from  the  bottle.     This  is  to  avoid 
laying  the  stopper  on  the  table. 

Inverting  and  shaking  a  test-tube,  Fig.  13.  4 

The  mortar  and  pestle,  Fig.  14.  5 


FIG.  13. 


FIG.  14. 


94          ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 

6  The  gas  generator,  Fig.  15. — T,  Thistle-tube  ;  D,  deliv- 
ery tube.  It  is  well  to  wet  glass  tubing  when  putting  it 
through  stoppers  or  connecting  it  with  rubber  hose. 

^  To  cut  glass  tubing. — Make  a  scratch  with  a  three- 
edged  file  where  it  is  desired  the  tube  shall  break.  Hold 
the  tube  in  both  hands,  the  thumbs  brought  together  on 
the  opposite  side  from  the  scratch.  Pull  the  hands  apart 
in  the  direction  of  the  tube's  axis,  with  only  a  very  slight 
bending  motion.  If  the  tube  is  short  or  the  glass  thin,  it  is 
well  to  hold  it  in  one  or  two  folds  of  the  towel.  Fig.  16. 

8  To  smooth  the  sharp  edge  of  a  cut  tube,  hold  the  end  in 
the  gas  flame  until  the  glass  softens.     Fig.  17. 

9  To  bend  glass  tubing,  hold  it  in  the  flame,  preferably  a 
wide  one,  twirling  it  between  the  thumb  and  fingers  until 
the  glass  is  thoroughly  softened,  then  slowly  bend  to  the 
desired  angle.     The  bend  should  be  smoothly  curved,  as 
seen  in  the  figure.     If  the  heating  is  insufficient,  or  the 
bending  too  hasty,  the  glass  wrinkles,  and  the  tube  is  likely 
to  break.     It  is  well  to  pass  the  tube  through  the  flame 
once  or  twice  after  it  is  bent,  so  that  the  cooling  may  be 
slow.     Fig.  18. 

10  To  draw  out  and  close  glass  tubing,  hold  it  in  the  flame 
until  the  glass  is  well  softened,  then  draw  apart  slowly  and 
to  the  desired  extent,  and  finally  heat  it  still  more  at  the 
separating  point  and  draw  again.     Fig.  19. 

11  Heating  a  crucible,  Fig.  20. — The  crucible,  C,  rests  on 
the  pipestem  triangle,  T,  and  this  in  turn  on  the  iron  ring 
of  the  stand,  S.     The  tongs,  X,  are  used  to  handle  the 
crucible  or  its  lid  while  hot. 

12  Evaporation  to  dryness  in  the  porcelain  dish,  D,  Fig. 
21. — When  there  is  danger  of  spattering,  it  is  well  to  hold 
the  burner  in  the  hand,  and  to  touch  the  tip  of  the  small 
flame  for  a  moment  to  the  bottom  of  the  dish.     The  pur- 
pose is  to  heat,  but  not  enough  to  cause  the  formation  of 
bubbles  of  vapor.     Constant  stirring  with  the  rod,  R,  is 
important. 


FIG.  19. 


FIG.  15. 


FIG.  17. 


FIG.  20. 


FIG.  21. 


96 


ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


13  Filtration. — Prepare  the  filter  paper  by  folding  it  across 
two  diameters  at  right  angles  to  each  other,  then  separating 
the  quadrants  so  as  to  form  a  cone,  d.     The  cone  should  be 
fitted  into  the  funnel  and  then  wet,  so  that  the  paper  ad- 
heres to  the  glass.     Fig.  22. 

Fig.  23. — Filtering,  pouring  the  liquid  from  the  beaker, 
B,  using  the  rod,  R,  upon  the  funnel,  F',  showing  the  stem 
of  the  funnel  lying  against  the  wall  of  the  beaker,  so  that 
the  liquid  which  runs  through  may  not  cause  spattering 
by  dropping  into  the  middle  of  the  beaker. 

14  The  graduated  cylinder,  Fig.  24,  to  use  in  measuring 
liquids;  content,  fifty  cubic  centimeters  (c.  c.). 


FIG.  24. 


FIG.  23. 


APPENDIX  97 

The  thermometer. — The  measurement  of  temperature  15A 
is  made  with  the  centigrade  thermometer.  The  fixed  points 
of  this  are  the  boiling  point  of  water  and  the  melting  point 
of  ice.  The  latter  is  made  0°  of  the  scale,  and  the  former 
is  made  100°,  the  space  between  the  two  points  being 
divided  into  one  hundred  equal  parts,  called  degrees.  In 
the  Fahrenheit  thermometer,  which  is  more  commonly 
used  in  matters  other  than  scientific,  these  two  points  are 
made  32°  and  212°  respectively.  The  relation  between  the 
two  scales  is  made  clear  in  the  diagram.  Fig.  25. 

Thermometers  are  fragile  and  expensive,  and  must  be 
used  with  care. 


J_op 


32 


BOILING  POINT 


MELTING  POINT 


FIG.  25. 


98 


ELEMENTARY  PRINCIPLES  OF  CHEMISTRY 


15B  The  barometer.  Fig.  26. — The  long  tube  is  completely 
filled  with  mercury,  then  inverted  in  the  shallow  dish  of 
mercury.  The  atmospheric  pressure  on  the  free  surface  of 
the  mercury  sustains  a  column  of  varying  length,  the  nor- 
mal being  760  millimeters.  Fig.  27,  the  siphon  form  of 
barometer. 


\VACUUM 


FIG.  27. 


FIG.  26. 


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